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Hardscape Edition 2013

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Concrete Masonry Designs Hardscape Edition 2013 | 1

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2 | Hardscape Edition 2013 Concrete Masonry Designs

Publisher: Robert D. omas

Editor: Randi H. Hertzberg [email protected]

Associate Editors: Dennis W. Graber, P.E.Gabriela Mariscal, P.E. Elena MorenoJason ompson

Design and Layout: Alison Dixon, ImagePrep Studio

Concrete Masonry Designs magazine showcases the qualitiesand aesthetics of design and construction usingmanufactured concrete masonry and hardscape products.Concrete Masonry Designs is devoted to design techniquesusing standard and architectural concrete masonry units,concrete brick, articulating concrete blocks, segmentalretaining walls, manufactured stone veneer and otherconcrete masonry products around the world. We welcomeyour editorial comments, ideas and submissions.

Copyright 2013 by the National Concrete MasonryAssociation. All rights reserved. Contents may not bereprinted or reproduced without written permission fromNCMA.

Concrete Masonry Designs is published by the NationalConcrete Masonry Association (NCMA), and distributedto advance and support the concrete masonry andhardscape industry and public interest.

Send address corrections and advertising inquiries to: NCMA Marketing and Communications 13750 Sunrise Valley DriveHerndon,VA 20171-4662703-713-1900 Fax [email protected]

Sign up for a Concrete Masonry Designs subscriptions atwww.ncma.org/cmdhardscapes.


RESIDENTIALResidential Retaining Walls

7 Gull Lake Residence9 Shook Castle 9 Eden Prairie Bluffs 11 Private Residence12 Outdoor Living

COMMERCIALTall Walls

22 As High as a Giraffe’s Eye24 Reaching New Heights in Cairo26 SRWs Score at Kansas Stadium28 SRWs Rise to Hilltop Challenges30 Razorbacks Practice in Private

FEATURES

DEPARTMENTS55 Q&A - When to Call a Design

Professional

58 SRW History Articles Series: SRW Design

60 New Product Profile - Carved in Stone

56 Marketplace

62 Continuing Education Learning Program


TRANSPORTATIONOn the Road

33 e Power of Purple34 Sound Wall Solves Interstate Widening Problems35 Homes Without Surround Sound 36 Cruising Interstate 75 38 A Pattern for Success

ACBsErosion Control andStormwater Managementwith ACBs

46 Ramping Up at Klamath 48 Erosion Control at the Lake Lamour Spillway 50 Revitalization of a Runoff Canal52 Lesson Plan: St. John’s College High School

7

18 40

32

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I’d like to take this opportunity to present NCMA’s newly redesigned

publication, Concrete Masonry Designs. This issue focuses on the industry’s

hardscape products. Our goal is to showcase the beauty of designing with

manufactured concrete products for the landscape market and give you an

understanding of the benefits to using these products. Segmental retaining

walls (SRWs), articulating concrete blocks (ACBs), and concrete masonry

fences not only provide solutions to many of today’s design challenges, but do

so in an aesthetically pleasing way.

Segmental retaining wall (SRW) units are concrete units that are placed

without the use of mortar (dry-stacked), and which rely on a combination of

mechanical interlock and mass to prevent overturning and sliding. The units

may also be used in combination with horizontal layers of soil reinforcement

that extend into the backfill to increase the effective width and weight of the gravity mass. Units are

available in a variety of colors, textures and sizes to meet the design teams’ goals. The articles within this

issue highlight the design flexibility, economics, durability, and performance of segmental retaining wall

units.

Articulating concrete blocks (ACBs) are a flexible revetment system that provide effective erosion control,

allow for water infiltration, and can also include plantings to maintain a natural appearance. ACBs are

effective and economical for a wide range of erosion protection, water flow rates, and are easily installed

above or below the waterline, as either cabled or non-cabled systems. The term “articulating” implies the

ability of the matrix to conform to minor changes in the subgrade while remaining interlocked with or

without the use of cables or geotextiles. The interlocking property provided by the ACBs’ special shapes also

allow for expansion and contraction.

Concrete masonry fences are used as sound barriers or privacy fences in residential and transportation

projects. New dry-stack systems allow for fast and economical installation. Concrete masonry offers

outstanding sound attenuation properties with the aesthetics designers want.

As you read the articles in this issue, you will learn that SRWs, ACBs, and fences offer an endless array of

possibilities.

I look forward to hearing what you think of our new publication!

Robert D. ThomasPresident

National Concrete Masonry Association

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Segmental retaining walls (SRWs) are modular concreteblock retaining walls used for vertical grade changeswith many residential applications. The walls are

designed and built as either conventional gravity retainingwalls or reinforced soil retaining walls. They are constructed ofdry-cast concrete units that are dry stacked (placed withoutmortar) and depend on their unit-to-unit interface and massto resist overturning and sliding. Unit-to-unit interfacesinclude friction, shear elements, and interlock. The systemscan also employ soil reinforcement that extends into thebackfill and allows for the construction of taller walls thancould be accomplished with the block units alone.

Segmental retaining walls are considered flexible structures, sofootings do not need to be placed below the frost line whenthere is sufficient foundation bearing capacity. SRW units are manufactured in conformance with industry standards and spec-ifications to assure that units delivered to a project are uniformin weight, dimensional tolerances, strength, and durability.

There is little restriction to the height of SRWs, and they canreach 50 feet (15.2 m), or more. In single-family residentialapplications, SRWs typically are more pedestrian in scale, yetjust as in multi-family projects and other commercial applica-tions, tall walls can be used to create vertical support of allheights for new, usable space above.

RESIDENTIAL

Residential Retaining Walls

Gull Lake Residence, Brainerd, MNProducer: W. W. Thompson Concrete ProductsLicensor: Keystone Retaining Wall Systems, LLCDesigner/Owner: Moe’s Contracting and LandscapingContractor: Moe’s Contracting and LandscapingGeosynthetic Manufacturer: SRW Products

Located on a high Birch Island bluff overlooking Gull Lake,this single-family residence had access to the water down asteep slope that had been shored up with a timber wall. Butover time, wood deteriorates, even pressure-treated wood. Dis-colored, rotting and sagging in places, the timber wall needed tobe replaced.

e solution was a concrete masonry segmental retaining wall.e SRW was used to manage the slope, hold back the soils,and create a variety of planters, gardens, stairs, landings andpatios at the top.

But the site presented some tough constraints. Nestled into itswaterside slope, there was very limited access to the propertyfor removing the old system and installing the new one. Sothe bottom half of the timber wall was demolished by handand removed by a barge along the lake. en the concreteblock units for the new, lower section were brought in thesame way.

e project had to be com-pleted with a minimumamount of excavation, so screw-in soil reinforcement anchorswere used. Once the dry-stackSRW system was installed onthe lower wall section, it wasimmediately secure and usable.e SRW-strengthened lowerslope could then support equipment for excavation andremoval of the top of the old timber system, and the upper portion of the SRWs and patios were completed. CMD

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RESIDENTIAL

Shook Castle,Sedalia, COContractor: Bear Retaining WallsProducer: Colorado Best BlockLicensor: Keystone Retaining Wall Systems, LLCDesigner: Anchor EngineeringGeosynthetic Manufacturer: TenCate Geosynthetics

Installation crews worked to correct erosion and stability concerns where a new home was being constructed on a scenic,but challenging site.

Cost-saving and aesthetic considerations were both high priori-ties for the homeowners as they considered their options. ehuman scale and inviting design of individual concrete masonryunits in a segmental retaining wall (SRW) would tame the steepsite and also maintain its residential character. e SRW systemselected is specifically designed for taller wall structures andheavy loading conditions. Having the multi-unit system manu-factured nearby added to the overall cost savings.

With the new residence already under construction, the wall in-stallation crew struggled with limited access to the job site, aswell as with the challenges of constructing a 5,000-square foot(464.5 m2) retaining wall in such close proximity to an unfin-ished structure.

e interlocking concrete block wall face offers the rusticatedlook and character of a random-patterned natural stone wall. Italso has many functional advantages. e core of the concreteSRW blocks are open and were filled with gravel and used as adrainage filter to help minimize hydrostatic pressure to the wall.Varied facing units contribute to the natural stone appearance,and at 8 inches (0.2 m) in height and 12 inches (0.3 m) deep, theyprovide stability for the tall walls. When completed, the SRWstructures created terraced walls with useable areas between them,along with plenty of space for plants at the single-family homeknown as Shook Castle.

Eden Prairie Bluffs,Eden Prairie, MNProducer: Anchor Block CompanyLicensor: Anchor Wall Systems, Inc.Contractor: TMS ConstructionGeosynthetic Manufacturer: TenCate Geosynthetics

Concrete masonry segmental retaining walls help maximize thepotential of a multi-family building site. Renters and homebuy-ers of luxury housing units have high expectations for attractiveamenities.

Residential developers are responding with upscale designs indurable materials. e tall walls at the multi-family complexEden Prairie Bluffs in Eden Prairie, MN, add usable space for aswimming pool and parking, along with privacy and security, toa landscape plan that appears derived from nature.

While single-family retaining walls are often gravity walls, on alarger project like Eden Prairie, the tall walls are more likely re-inforced with geogrid. SRW walls on the project are constructedwith a multi-colored block in a combination of sizes that mimicsthe random look of hand-stacked stone walls.

Initial cost and life-cycle cost play a large role in material sys-tems selection in larger buildings, and masonry SRW systemstypically come out ahead. Maintenance is an ongoing challengein multi-family complexes, so the durability of concrete segmen-tal retaining walls means fewer repairs, plus integrally coloredmasonry will not fade, rust or discolor from the weather.


RESIDENTIAL

retaining walls contributed to the economy and constructionefficiency of the project.

e sharp vertical drop and lakeside location presented construction challenges. e 2,000 square feet (185.8 m2) ofconcrete walls were built in stages. In all, 17 dump trucks ofearth were removed. en once the wall construction started,that dirt needed to be replaced.

Although the installation logistics were challenging, the proj-ect was a success. With a crossover ramp and a grand stairwayas the focal point, access between the house and the lake isseamless. And patios create large areas for dining and entertaining.

Private Residence, Penticton, British ColumbiaEngineer: Chris Hudson (owner)Producer: ExpocreteLicensor: Allan Block Retaining Wall SystemsContractor: Block by Block Landscaping, Ltd.Geosynthetic Manufacturer: Strata Systems, Inc.

An extensive series of walls were built on this lakefront sitein Penticton, BC. e steep slope against a backdrop of ex-isting homes meant that the project needed to be completedby hand. e selection of concrete masonry segmental


RESIDENTIAL

Concrete masonry segmental retainingwalls (SRWs) offer many advantages ina residential hardscape design. From

identifying the boundaries of an outside room,to establishing a series of raised patios, built-inbenches, gardens and planters, to elevating aslope that extends a backyard’s usable space,SRWs and stairs are increasingly providingresidential design solutions that bring theindoors outside. Selected for their strength,durability, and maintenance-free features, alongwith their varied and beautiful aesthetics,SRWs are a mainstay today in the upscaleluxury home market.

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RESIDENTIALK

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are giving homeowners newrooms outside for relaxing and

entertaining. One of the most popularspaces is the outdoor custom kitchen. Aconcrete masonry outdoor kitchen is awonderful way to add living space to aresidence. It can be as simple as theaddition of a fireplace with grill or afull-fledged kitchen and dining roomthat blurs the distinction of interior andexterior rooms, merging everything intoone pleasant space.

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RESIDENTIAL

As more people choose to spend their free timerelaxing at home, incorporating swimming poolsinto a resort-like setting is one of the latest trends.

Concrete masonry walls and patios define these spa-basedretreats, offering beauty, durability, safety and privacy.Waterfalls, fountains, and other natural-looking waterfeatures help contribute to the backyard feeling ofvacationing in a far-off location.

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RESIDENTIAL

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RESIDENTIAL

Fire features built of concrete masonryoffer homeowners more time outdoorsby creating both firelight and warmth

when temperatures are cool. Some options forincorporating a fire feature into outdoor spaceinclude an outdoor fire pit, a fireplace, and firetables, all inviting additions to an outdoorliving space. CMD

Fire Pits &

FirePla

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RESIDENTIAL


But slope support is only one of the benefits offered by SRWs.The ability to create more space, where none existed before,can make concrete block segmental retaining walls a powerfuldevelopment tool. The walls are designed and constructed asconventional gravity retaining or reinforced soil retainingwalls, and they are increasingly employed to support parkinglots, playgrounds, drives and roadways, patios, and even thesurrounding areas of some buildings. The uses for SRW systems continue to multiply.

The basic elements of a segmental retaining wall system arefoundation soil, leveling pad, interlocking concrete block units,retained soil, gravel fill, and soil reinforcement when required.SRWs can be designed with straight lines or curves, have stepsand turn corners, and are manufactured in a wide variety ofcolors, sizes, and textures.

COMMERCIAL

Segmental retaining walls (SRWs) are systems of modularconcrete blocks interlocked with one another to hold backthe soil of a slope at grade changes where the front of the

wall is vertical or near vertical. They prevent the soil on a slopefrom sliding down. Due to their locking mechanisms, tall andsteep SRWs can effectively restrain the lateral forces applied bybackfill soils.

Designing tall walls with segmental retaining wall unitscreates additional usable space on project sites.

Cairo(see page 24)


An SRW system consists of dry-cast concrete units that areplaced without mortar (dry-stacked) and rely on their unit-to-unit interface and inherent mass to resist overturning and sliding through friction, shear, and interlock. Yet, SRWs couldnot reach tall heights with only concrete block units. By ex-tending soil reinforcement into the backfill, it is possible toconstruct walls as high as 50 feet (15.24 m) or more, as wasdone throughout the walls that surround the 1100-acre (445-hectacres) Uptown Cairo, a immense multi-use development(see Reaching New Heights in Cairo). Similarly, a new entranceat the Cincinnati Zoo was only possible when new space wascreated with the backfill behind a large, tall retaining wall (seeAs High as a Giraffe’s Eye).

Segmental retaining walls are considered flexible structures, soa footing does not need to be placed below the frost line pro-vided there is sufficient foundation bearing capacity. SRWunits are manufactured in conformance with industry stan-dards and specifications to assure that units delivered to a project are uniform in weight, dimensional tolerances,strength, and durability.

reaching out and upTall walls often have special concerns that do not come into play for short walls. Given their height, tall walls will

influence, and be influenced by, a much larger portion of a site,so project designers must carefully address site conditions be-yond the location of the segmental retaining wall face andbelow it. Layout issues, such as the wall batter and geosyn-thetic reinforcement lengths, become more significant with tallwalls that occupy more space and in turn, need more space forlonger reinforcement lengths.

COMMERCIAL

n Learn to describe a segmental retaining walland its components

n Understand settlement and how backfill andgeogrid stabilize SRWs

n Explain the height limits for tall SRWsn Discuss the design considerations for tall SRW

walls in creating additional horizontal spaceabove.

C E U : L E A R N i N G O b j E C T i v E S


Segmental retaining walls have a facing component and a sta-bility component. The facing part of the system includes theindividual concrete block units that lock together and are at-tached to restraining members. The restraining members aretypically geogrids buried in the backfill. By attaching to thestable area of the soil, the geogrids support the wall and alsostabilize the soil behind the wall, overcoming toppling forcesand allowing construction of higher and steeper walls. At theLawrence, KS, stadiums, three sets of masonry bleachers sup-ported with extensive geogrid, along with a fourth vertical setwere built in less time and for a lower cost than a competingaluminum system (see SRWs Score at Kansas Stadiums).

Post-construction settlement of reinforced infill soil is a pri-mary concern for tall walls. Even well-compacted, high-qualitygranular backfill will settle after construction. Minor amountsof settlement become an issue for tall walls: When the backfillsettlement is less than 1 percent of the fill height, it can add upto a significant amount of settlement in 30-, 40- or 50-foot(9.14-, 12.19- or 15.24-m) high walls. Total settlement of wallbackfill affects the performance of any structures above thewall, such as pavements. Also, the possible differential settle-ment between the wall face, which is made of uncompressibleconcrete SRW units, and the wall backfill soils is an issue fortall walls because the differential settlement increases withheight. The backfill, and the geosynthetic layers within it, maybe pulled down and out of the SRW units as a result, poten-tially damaging the geosynthetic or else overloading appliedforces at the SRW unit-geosynthetic connection.

There are some proven design strategies used to counter thissettlement issue, such as soil compaction. Increasing relativedensity compaction requirements to 95% Modified Proctor or98% Standard Proctor can help. So, too, can encouraging con-sistent compaction quality, through quality control and qualityassurance requirements. More frequent compaction testingmight also be needed for tall walls compared to shorter walls.Installation practices that lead to top performance in shortwalls are not always enough for tall walls. Gravel fill and level-ing compaction, and alignment tolerances need close attentionto provide acceptable results for taller walls.

Adjusting the width of gravel fill behind the SRW unit face upto 3 feet (1 m) can accommodate the differential settlementbetween the units and reinforced backfill soils. Sometimesgravel fill thickness is also graduated throughout the wall

COMMERCIAL

Cincinnati Zoo(see page 22)

Kansas Staduim(see page 26)


height. For example, for a 45-foot (13.7-m) wall the gravel fillmight be 3 feet (1 m) thick gravel for the bottom 15 feet (4.5m), 24 inches (610 mm) for the middle 15 feet (4.5 m), and 1foot (305 mm) thick for the top 15 feet (4.5 m) of wall.

Attention to the quantity and quality of fines in the soils canhelp. Decreasing the plasticity index (PI) of fine fraction ofbackfill soils down to a PI of less than 5 to 10 is one approach.Requiring select granular backfill in the reinforced zone thathas no more than 5 to 15 percent fines is also a good idea.

Tall walls require special attention to internal and surfacedrainage. Breaking a single tall wall into two tiered walls likethe approach taken for the MasterPark expansion near theSeattle-Tacoma International Airport (see SRWs Rise to HilltopChallenges), where the upper wall gets set back no more than afew feet (meters), does not significantly alter wall loads or re-inforcement requirements, but it does allow the wall contractoran opportunity to reset the wall face alignment and reduce thedifferential settlement between the upper SRW units and thewall backfill.

The success of these strategies to avoid settlement issues, aswell as what value in these criteria ranges should be used, de-pends on the height of the wall, the on-site soil and fill soiltypes available, the accuracy of the site and materials data, localexperience, anticipated quality control of installation, and en-gineering judgment. As an example of the range of judgment,tall walls backfilled with on-site, fine-grained soils are com-monly successful in some regions, while in other regions thenative soils properties make fine-grained soils unsuitable as fillfor even 10-foot (3.05-m) high walls.

While technically the height of SRWs is limitless, from apractical point of view, experience with very high retainingwalls [greater than 50 feet (15 m)] is indeed limited. AlthoughSRWs have been successfully built in excess of this height, theknowledge and experience of their behavior is still being col-lected. New and unique challenges will likely be confronted atthese heights. CMD

COMMERCIAL

Seattle-Tacoma international Airport (see page 28)


The Cincinnati Zoo & Botanical Gardens is the secondoldest zoo in the United States, and its limited space ina central city location was imposing conflicts between

the need for exhibit areas and the need for visitor parking.With attendance on the rise, the Zoo purchased additionalland with plans to relocate the entrance, add 400 parkingspaces and provide space for new exhibits.

In 2009, the Zoo opened its $19.6 million entrance, designedto make the park more visitor-friendly. Consulting engineersM•E Companies, Cincinnati, transformed a 12-acre (4.9-hectacres) urban site with a variety of problems into agateway entrance and parking lot for the Zoo and helpedspark redevelopment efforts in the area. One of the biggest

issues with the purchased property was its sunken location incomparison to the Zoo. The challenge became how to get vis-itors from the new parking lot, across busy Vine Street, andsafely into the Zoo, which is located 22 feet (6.7 m) above theparking area.

M•E Companies designed a 25,000-square-foot (2,322.6-m2)segmental retaining wall (SRW) to raise the site and support a pedestrian bridge, which allows visitors to cross the busystreet without interruption from traffic. The tall SRW alsogives the Zoo room for an expanded entry plaza and space forThe Historic Vine Street Village, where visitors can relax, eatand shop. This new area created by the wall also provides roomfor ticketing, guest relations, membership and retail spaces.

As HIGH as a Giraffe's Eye

COMMERCIAL


The new entrance had an added benefit as well. It enabled theZoo to continue its commitment to being green and preserv-ing the environment. With the addition of the retaining wall,the zoo was able to expand its footprint and gain additionalspace needed to collect and store millions of gallons of rainwater from underneath the 30,000 square feet (2,787 m2) ofpermeable pavers that greet visitors as they enter the Zoo.Captured rain water is used to irrigate the surrounding land-scape. Living up to its reputation as the “Greenest Zoo inAmerica,” Cincinnati Zoo applied for and received LEED NCPlatinum certification for the project.

Cast-in-place piers that support the pedestrian bridge are em-bedded more than 40-feet (12.2-m) deep into sloping bedrock.One of the construction challenges was to incorporate theSRW with the piers that support the pedestrian bridge. At thepier locations, a portion of the wall rests on the pier footingwhile the remainder of the wall resides on compacted granularbase. Extra care in subsoil and base compaction was needed toprevent differential settlement at these locations. Higher levels

of compaction were achieved by decreasing the normally rec-ommended 6 to 8-inch (152 to 203-mm) lifts to 4 inches (100mm), and performing multiple passes with compaction equip-ment. And, elevating the new entrance with support from atumbled ashlar-patterned segmental retaining wall gives theappearance of hand-laid stones.

The project has been successful on many counts. It is easy toenter and exit the new parking area, so traffic congestion isminimized, and with more parking available, visitation in-creased. There is a clearly defined and inviting new gateway tothe Zoo that makes the arrival experience enjoyable. In addi-tion, there is now room for future facilities at a Zoo with nomore land available.

The Zoo owners felt that the combination of cost, aestheticsand flexibility of the segmental retaining wall provided thebest overall value for their project. “We couldn’t be happierwith the finished product,” said Cincinnati Zoo & BotanicalGardens’ spokesman Mark Fishers. CMD

COMMERCIAL

Cincinnati Zoo & BotanicalGardens, Cincinnati, Oh n Consulting Engineer: M•E Companiesn General Contractor: HGC

Constructionn Contractors: Outdoor Environments,

Inc; Mainline Bridge; Performance Site n Architect: Cornette/Violetta

Architects, LLCn Producer: Reading Rock, Inc.n Licensor: Allan Block Retaining Wall

System


Egypt has long been known for its awe-inspiringmonuments and structures. Now, the mixed-usedevelopment Uptown Cairo adds yet another impressive

landmark to the Egyptian landscape. Perched atop ElMokattam Mountain at 650 feet (200 m) above the city,Uptown Cairo encompasses a series of 11 villages on a site thatspreads over more than 1100 acres (445 hectacres). And all of itis entirely surrounded by a segmental retaining wall (SRW) thatin some places reaches 65-feet (20-m) high.

Created as a small city with its own neighborhoods, within thegreater city, Uptown Cairo is one of the first large-scale masterplanned communities in the Egyptian capital. With panoramicviews of the city, a main attraction of the residential, retail,business and resort development is its high elevation. But theterrain at this mountaintop site was variable, and ranged fromgentle to steep slopes. A network of natural erosion gullies calledWadis spread throughout the desert site, with sharp, shallowdepressions separating the land. The plan calls for both low-riseand high-rise structures, with lower buildings, such as single-family homes and townhouses, at the top of the site’s summitsand peaks, while taller buildings ranging from three to 22 storiesare positioned lower down the mountainside.

In order to create enough additional flat areas to make space formore residential properties in the prime locations near the topof the peaks, a system of strong walls was required. Borders ofthe gated, urban villages are rendered by the roads that surroundthem, with their interior roads and walkways linking back to theneighborhood-defining loops.

“A segmental retaining wall system was selected for the UptownCairo project due to the topography of the mountain and to thelarge difference in elevations between the compound’s villas andthe roads,” said Dr. Nagui Riad, general manager and owner ofCairo-based GEOS Co., the wall contractor and blockproducer. And the SRW system held out other benefits, as well.

In general, the structural stability of SRWs is improved byincreasing the wall batter. Batter is the setback between theSRW units from one course to the next. In most cases, thebatter is controlled by the location of shear pins or lips on theunits, although some systems allow adjustments to the batter.And taller walls typically have a greater degree of batter.However, according to Riad, the proprietary system used atUptown Cairo had an advantage over other systems. It allowedconstruction of basically vertical walls, and this greatly increasedthe area of land available to be sold to clients, he said.

COMMERCIAL

Reaching New Heights in Cairo


The decision to specify segmental retaining walls was also basedon economics. The SRWs were more economical than acompeting concrete retaining wall by 20 to 40 percent, estimatesRiad. And one more bonus was the great architectural aestheticachieved with the individual blocks and caps.

tall Walls, tall OrderThe SRW system at Uptown Cairo is unique in that it makes atrue mechanical connection, thus keeping the wall intact in caseof any seismic activity, or any lateral movement, according toRiad. And he says, it also has a great factor of safety forfoundation soil and for all other variables that have directimpact on the retaining walls.

It is possible to create a single tall wall of great height thatperforms with great success. However, differential settlementbetween a wall face of uncompressible concrete SRW units andbackfill soils can increase with wall height and can be an issuefor tall walls by threatening the geosynthetic connection. Onestrategy design professionals use to avoid this is to break thesingle tall wall into a multi-tiered wall, with upper walls set backno more than a few feet (m) from the one below. This does notsignificantly change the loads on the walls or the reinforcementrequirements but it offers the opportunity to reset the wall facealignment and reduce differential settlement between the upperSRW units and the wall backfill.

At Uptown Cairo, some walls reach 65 feet (20 m) in height.GEOS divided many of those walls into four, 16-foot (5-m)steps each. There are also 49-foot (15-m) high single walls thatare performing well. Overall, the tall walls provide the additionalspace desired and contribute to the defining aesthetic of theproject.

Not only did the mountainous landscape dictate the need forthe massive retaining wall, it also presented issues duringconstruction. “In some areas, especially at the top levels of thewall, backfilling work was very hard, as there was no access forthe equipment, except from the top of the mountain,” Riad said.

Active Brain Consulting Group (ABCG), an integratedconsulting engineering firm in Egypt, specified 500,000 squarefeet (4,645.2 m2) of beige structural SRW products for theproject. Not only did straight-faced units allow for flexibilitywithin the design, easily accommodating curves, but the pinsystem used dramatically minimized the overall constructiontime, according to Riad.

The ever-changing terrain surrounding the Uptown Cairodevelopment presented a few challenges during construction.Some elevations required the use of more SRW units than otherelevations; thus, requiring more backfill in some locations. Inaddition to delivering the units and backfill materials up themountain side, excavating the entire project out of the rocky El-Mokattam hillside proved challenging. GEOS installers worked24-hours-a-day, sometimes completing 2,000 square feet (185.8m2) of wall a day. Construction on the multi-phase developmentis still in progress, and the final construction phases includehotels, resorts and more downtown buildings. CMD

COMMERCIAL

uptown Cairo, Cairo, egypt n Designer: Active Brain Consulting Groupn Landscape Planner: Wimberly Allison Tong

& Goon Architects: Wimberly Allison Tong & Goon Contractor: GEOS Co.n Licensor: Keystone Retaining Wall Systemsn Producer: GEOS Co.

Gravel Fill

Gravel Fill


With the football season less than a year away, andtwo high schools with no available stadiums, theLawrence, KS, school district had a dilemma. They

needed bleachers at both schools before the next school yearstarted.

As soon as Landplan Engineering of Lawrence was retained todesign and oversee construction of a $21 million project thatencompassed the two football stadiums, along with baseballfields, tennis courts with seating, softball fields, soccer fields, andparking for more than 1,050 vehicles, they turned immediateattention to the stadiums. The plan was to design the stadiumsfor both schools with aluminum bleachers, much like thosecommonly found at schools and universities around the country.

But aluminum bleachers could not meet the Lawrence SchoolDistrict’s timing, according to C.L. Maurer, senior landscapearchitect with Landplan’s Lawrence office. “The aluminum

bleachers would be designed and ordered in December, shopdrawings sent in January or February, revisions to shop drawingsin March and April, and then a minimum of another six toeight months would be needed to fabricate and deliver them tothe site. That would be about one year,” he said. One year meantthat the entire football season would not be accommodated.

About the same time, a local manufacturer representative fromCapitol Concrete Products gave the designers a presentation onusing segmental retaining wall (SRW) units for landscapeprojects. Immediately, the idea to use SRWs as the bleachers’structure took shape. SRWs could provide the structure andvertical faces, with pavers specified for the seating rows.

For safety reasons, the school district was requesting enclosedbleacher seats instead of an open design. Cost estimates for theenclosed aluminum bleachers came in at $400 per seat, whileSRW bleachers would average about $300 per seat.

COMMERCIAL

SRWs and pavers provided the most cost-effective and efficient solution over aluminum bleachers.

SRWs Score atKansas Stadiums SRWs Score at

Kansas Stadiums


In addition to a cost savings of about 25 percent, the blockbleachers would be much quieter than aluminum bleachers.Noise abatement at the stadiums was a concern in theresidential neighborhoods where the two schools are located.

And there was a passive solar component to the SRW bleacherapproach, as well—the masonry bleachers would collect heatfrom the sun during the day and radiate thermal energy outlater in the day. That was an added benefit of the block systemover aluminum, especially on cold October evenings.

Stormwater management was also a concern with an enclosedbleacher system. The aluminum approach would have includeda series of gutters to move the water away from the bleachers.With the SRW bleachers, the engineers originally planned tomove water away through PVC pipe and gravel to a lower ‘piperoom’ in a 10-foot by 10-foot (3-m by 3-m) concrete bunker.But, says Mauer, the space would need to be maintained, andthus was considered an occupied area. Local codes called for thepipe room to have a sprinkler system, which would have pushedthe project over budget. Instead, the rows of block seats weredesigned with a slight incline where the center is the high pointof the bleacher rows, so that water drains down the rows and outboth sides.

The Free State High School and Lawrence High Schoolprojects each included two sets of bleachers. Three of thebleacher sites allowed for construction of partially terracedberms to support the structures from behind. But the fourthset backed up to a parking lot at Lawrence High School,presenting no opportunity for backfill or earthen support.Instead, a near-vertical wall was built to support this bleacherset, providing seats for 4,000 fans. The terraced bleachers werebuilt on dirt hills covered with 2 feet (609 mm) of clean gravel.As the bleacher rows were added, more dirt was placed andcompacted on the hill. Geogrid was installed every third block,Mauer said. And the geogrid runs under each seat row. A 50-foot conveyor was used to deliver drainage gravel over the topof the 16-ft (4.9-m) wall.

Bleacher walls were built up with more than 65,000 square feet(6,038 m2) of block before pavers were installed on the seat rowsto avoid damage to the pavers during wall construction. SRWcap units were used for seating. Because the non-terracedbleachers dropped 16 feet (4.8 m) off the top of the back wall,railings were secured to a series of 3-foot-square (0.91-m)reinforced concrete posts that run along the top of the verticalwall for the entire length of the structure.

Landplan designed the stadiums using segmental retaining wallmaterials, which to their knowledge were the first of their kindused in engineering structures. While performing the basicdesign in-house but recognizing the issues inherent in anygroundbreaking design, Landplan initiated an intensive reviewby outside firms to ensure the performance of the facilities forthe Lawrence school district.

Mauer said the four sets of bleachers were completed on anextremely fast track basis. Planning began in October; theconstruction document design for early elements started inJanuary, and construction of the stadiums’ seating began inSpring, and continued at a rapid pace during the summer. CMD

COMMERCIAL

high school Bleachers, lawrence Ksn Owner: Lawrence, KS School District n Designer: Landplan Engineering, P.A. n Contractor: BC Hardscapes LLC; VF Anderson

Builders LLCn Producer: Capitol Concrete Products, Inc.n Licensor: VERSA-LOK Retaining Wall Systemsn Geosynthetic Manufacturer: SRW Products, Inc.


Balancing the constraints imposed by two borderingmain roadways, by neighboring properties, by localauthorities for stormwater management, and by the

need to maximize the number of parking spaces serving amajor airport, all on a very restricted site, was anything buteasy. But MasterPark Lot C in SeaTac, WA, has succeeded onall fronts.

Mitigating the limitations of a dense area is never easy. Morelong-term, off-site parking was sorely needed for passengersheading to the Seattle/Tacoma International Airport. But,there was very little ground available. With a funeral home andcemetery right next door, the solution would need to be asunobtrusive and respectful as possible. The new lot also neededto be connected to the existing parking areas already on theMasterPark property. Finding a cost-effective means ofcreating a grade change greater than 30 feet (9.1 m) within asteep slope was the key to meeting these challenges.

A tall segmental retaining wall (SRW) was the answer,according to Tyler Gillis, owner of Sound Retaining Walls,Tacoma, WA. Spanning 1,100 feet (335.3 m), the SRW risesto 32 feet (9.8 m) in some sections and it holds up a parkingsurface for 659 cars, sitting well above the neighboring BonneyWatson Memorial Park. Location, aesthetics, and function

COMMERCIAL

MasterPark, lot C expansion, seatac, Wa n Designer: Sound Retaining Wallsn General Contractor: Goodfellows Brothers, Inc.n Engineers: Theis Engineering, LLCn Producer: White Block Co., Inc.n Licensor: Westblock Systemsn Geosynthetic Manufacturer: Strata Systems

SRWs solve parkingchallenges.

could all be accommodated with the segmental retaining wall.Only one issue remained.

In addition to its majestic mountains and its waterfrontlocation, the Seattle area is known for receiving a large amountof rain. Local regulators were concerned about runoff from theparking lot and insisted on a drainage system. But there werealmost no options available. Stormwater could not run off to

SRWs Rise to Hilltop Challenges


the memorial park, or to the highways, or to the parking areasbelow. That left only the SRW side of the project available fordraining stormwater runoff. “It is not normal to deliberatelysend water to a retaining wall,” Gillis said. “It is unusual topump water to the wall.” But that is what they did.

Sound Retaining Walls worked with the engineers on theproject by specifing a large system of 24-inch (609 mm)diameter pipes, every 20 feet (6.1 m) along the wall. A wide,curving access wall runs into and through the wall. Drainage isintegrated into the system with a 3:1 sloped landscape arealocated between two 16-foot (4.9-m) tiered walls that end at30-foot-high (9.1-m) corners, one curved and one at a 90-degree angle to the wall face. The runoff is piped to catchbasins 20-feet (6.1-m) wide and 30-feet (9.1-m) deep, withinthe walls to drain away the potentially destructive water,according to Gillis.

The curved wall corner required some special treatment. "Thewall batter actually works against you with walls this tall andeventually the radius at the top is too small. The solution,"

COMMERCIAL

says Gillis, "is to cut the blocks along the curve as needed andmortar them in place."

“The MasterPark job, with 20,000 square feet (1,858.1 m2) ofwall for a private owner was highly competitive due to therecession. The reason we won this project was ultimately theprice we could deliver it at. We used 1.33 square foot (0.12 m2)block, which is a big trend in the industry. That size blockpalletizes more efficiently than the old, conventional 8-inch by18-inch blocks (203 by 457 mm),” Gillis says. “Labor is lessexpensive and faster using a 1.33 unit and boosts productivityby 33 percent.” It took only three months to build.

Despite tight constraints and sensitive areas surrounding oneof America’s largest and rapidly expanding airports, engineerssuccessfully satisfied all the owner’s needs. CMD


COMMERCIAL

university of arkansas at razorback Field,Fayetteville, arn Architect: Polk Stanley Wilcox Architectsn General Contractor: Flintco Constructive Solutionsn Fence Structural Engineer: Kenneth Jones &

Associates, Inc.n Contractor: Walker Masonry & Sons Inc.n Producer: Midwest Blocks and Bricks n Licensor: Allan Block Retaining Wall System

University of Arkansas (U of A) stands out with anationally ranked football team. Since 1894, footballhas been an important part of the university and its

culture. When the decision was made to expand the footballfacilities at the school, a double-sided practice field wasincluded. And, to keep their practices under wraps at the U ofA Razorback Field, where the Southeastern Conference teampractices daily, a 7-foot-high (2.1-m) concrete masonry fencewas installed. Completely surrounding the two practice fields,the privacy fence creates a visual barrier that keeps the team’sprogress, plays, and practices confidential and provides securityin elevated areas.

In order to construct the new football operations building, theRazorback practice fields needed to move to the south side ofan existing building; a daunting task when space is limited.Polk Stanley Wilcox Architects of Fayetteville, AR, took ahard look at available space and decided there was no optionbut to build the football practice fields and the parking lot onthe same site and in the same location. The resulting designcarefully blends the two areas into one integrated facility.

Razorbacks Practice in Private


The fence system traces the perimeter of the two, full-sizedpractice fields, providing both privacy and safety, said BradMiller with structural engineering firm Kenneth Jones & Asso-ciates, Inc., Little Rock, AR. Pads are attached to the inside toprotect players. Both practice fields are elevated approximately14 feet (4.2 m) above the surrounding street level grades withan approximate fence height of 7 feet (2.1 m) above the playingsurface. The west practice field is on grade and the east practicefield is supported on a concrete deck with parking below. Halfof the fence is supported on grade and the other half on an ele-vated concrete deck. “The system was considered a less expen-sive and more aesthetically pleasing alternative to traditionalcast-in-place concrete stem walls,” Miller said.

It was necessary to incorporate the design of the garage withthe design of the fence above, in keeping with the school’smaster plan. The parking lot structure has large cast-in-placeconcrete columns, which extend from the ground to the top ofthe fence as posts. Brick-clad columns and posts create aseamless look and tie the new construction into the visualidentity of the university campus. Brick fence posts and con-crete masonry panels fill the space between the large columns.

The wall is a dry-stack, mortarless concrete masonry systemconsisting of end posts and fence panels. Reinforcing andgrouting requirements are minimal and are only required atbond beams and end posts. Footing requirements are alsominimal compared to traditional cast-in-place concrete, withthe entire load being resisted by footings at the posts. Only asmall leveling pad is required beneath the fence for the portionof fence constructed on grade. For the part built on the ele-vated concrete deck, the deck serves as both the leveling padand primary support at each end post, according to Miller.

Due to the height of the fence system above grade, careful at-tention was paid to wind loads on the wall layout with regardto bond beam quantity and spacing of end posts. The layout of

the system was optimized with bond beams located at the top,middle, and bottom of the fence height and end posts spacedapproximately 14 feet (4.27 m) apart. The fence system trans-fers wind loads horizontally to the end posts through the interlocking fence units and integral bond beams.

Although a portion of the fence was constructed on grade anda portion on elevated concrete deck, design procedures re-mained the same with special consideration given only to themeans of anchoring the end posts. Where the fence was builton grade, the fence posts were doweled to establish footingswith hooked dowels. Fence posts on the elevated deck weredoweled to post-tensioned concrete beams with hooked dow-els turned toward the interior of the structure due to thefence’s proximity to the edge of the concrete deck.

Another unique design feature was that the standard footingsfor the fence were modified when they were on top of theparking structure. There was no room for standard depth postfootings, therefore, the engineer on the project had to designthem as an L-shaped cantilever and extend the rebar backunder the playing field.

The end result is a beautiful concrete masonry privacy fencearound the football practice field and an integrated parkingstructure that work together to keep the Razorbacks on theirgame. CMD

COMMERCIAL

Detail of bond beams and foundation of the privacy panels at Universityof Arizona Razorback Field.


the Powercat retaining wall at the Kansas State University(The Power of Purple) are exposed to freezing and thawingconditions and are produced specifically for the requirementsin their state. SRW units produced today for use in allenvironments far surpass the performance of those in thetransportation marketplace a generation ago.

Sound barrier SRWs are used to reduce the impact of trafficnoise on properties adjacent to major urban highways. Becauseconcrete masonry possesses many desirable features andproperties—excellent sound attenuation, low-cost, designflexibility, structural capability and durability—it is anexcellent choice for the design and construction of highwaysound barrier walls.

Aesthetics is also an important consideration. Noise barrierssignificantly impact a highway's appearance and thus theexperience of the people in the vehicles using that throughway.Visual qualities of noise barriers include overall shape, endconditions, color, texture, plantings and artistic treatment. Thevariety of concrete masonry surface textures, colors andpatterns has led to its extensive use in sound barrier walls.Special color considerations helped drive the decision tospecify SRWs for the Kansas Powercat walls. Sound walls aretypically seen from two sides: the roadside and the occupiedside, as in Louisiana (Sound Wall Solves Interstate WideningProblems). In addition to noise abatement, the walls can be used to provide privacy for the developments and sitesbehind them. More commonly known as fences when used for privacy, they are built in the same manner as sound abatementwalls. CMD

TRANSPORTATION

On the RoadH ighway projects are put in use with long-life

expectations, requiring them to be durable andeasily maintained. Products such as segmental

retaining walls and fence products have proven to be bothreliable and durable for many transportation applications.

Segmental retaining walls (SRWs) are now being widelyadopted by transportation and highway markets throughoutNorth America. Retaining wall systems have been in serviceand successfully performing for a quarter century as viablealternatives to cast concrete or conventional earth retentionprecast panel wall systems with steel reinforced soils.

Today, state highway departments often specify SRW systemsfor their low initial cost compared to alternative systems, andalso for their more appealing aesthetics. The bridge abutmentsand retaining walls at the Cattlemen Road Extension(Cruising Interstate 75) in Sarasota, FL, were built with SRWsonce the decision was made to provide a faster, more attractiveand seamless look to the project. An added benefit was thereduced cost compared to the originally specified system. Atthe same time as they consider cost and aesthetics, governmentagencies are looking to reduce long-term maintenance needsand thus focus on overall life-cycle cost and durability.

In northern climates, some states have questioned the servicelife of SRW units under freeze-thaw conditions and to addressthat concern, require more stringent properties to beincorporated into the units. While this is not an issue in allstates, the industry and the Federal Highway Administrationjoined forces to research freeze-thaw performance of SRWunits. The products used in transportation projects such as theSouth Academy Boulevard Ramp (A Pattern for Success) and

SRW systems provide numerous advantages in thetransportation market.


TRANSPORTATION

feet (4886.7 m2) of segmental retaining walls (SRWs) for theirdurability, function, and sound-absorbing qualities. But therewas another reason, as well—aesthetics. And on the KansasRoute 18 retaining walls, the most important aesthetic thatblock offered was its ability to be integrally colored.

e Powercat logo is rendered in purple in otherwise beigeSRW walls on two sides of the roadway. KDOT did not wantto stain or emboss the emblem, thus eliminating competingwall systems, and instead choosing concrete units for theirability to be colored throughout. e integrally colored blockwould avoid maintenance and wearing issues in the future. Inresponse to KDOT’s request, the block manufacturer created acustom purple color recipe. Samples were shipped to the proj-ect personnel and then fine-tuned. As a result, the color wasmatched to the Powercat logo, and the school spirit is promi-nently displayed along this important thoroughfare. CMD

the Power of PurpleKansas Route 18 Powercat Retaining WallsOwner: Kansas Department of TransportationContractor: Leick ConstructionProducer: PavestoneLicensor: Anchor Block Company

When a large-scale construction effort to expand KansasRoute 18 was initiated, a series of six retaining walls and soundbarriers were required where the road and off ramp run alongthe Kansas State University campus.

Football at Kansas State University is an important part of theschool’s culture, and that culture reaches out into the localcommunity in Manhattan, KS. As a member of the Big 12Conference, Kansas State University’s Powercat logo is asource of pride and also instantly recognized around the coun-try. erefore, the Kansas Department of Transportation(KDOT) and the city of Manhattan selected 52,600 square


Baton Rouge, an active freight travel zone and a main east-west gateway to the south.

Specifications for the Interstate 10 widening project called fora large sound wall. One requirement was that the wall helpmaximize available space with near vertical construction. Inaddition, the miles-long wall needed to be durable enough towithstand the elements associated with a heavily traveledhighway. e wall, or fence, was built of concrete masonryunits, offering aesthetic appeal on both sides, and providingexcellent sound reflective properties.

e concrete block units were the transportation department’smaterial choice for constructing the sound wall, which rangedfrom 8 feet (2.4 m) to 16 feet (4.9 m) in height. Overall, it wasa versatile, durable and cost-effective wall system that easilyadapted to the challenges of the varied highway site. CMD

TRANSPORTATION

interstate Route 10 Widening ProjectProducer: Premier Concrete Products, Inc.Engineer: Lyver Engineering & Design, LLCLicensor: Keystone Retaining Wall Systems

Nearly 73,000 motorists travel along the Interstate 10 corridorthat stretches from Interstate 12 to Siegen Lane in BatonRouge, LA, almost every day. As part of the Louisiana Depart-ment of Transportation Development’s Geaux Wider program,the once four-lane stretch of highway reopened in February2013 with six traffic lanes; three in each direction. GeauxWider is a $315 million multi-year construction project in-tended to boost traffic capacity, increase safety and improvemobility on close to 20 miles (32.2 km) of Interstates 10 and12 in East Baton Rouge and Livingston parishes. I-10 is animportant route for the many people who live and work in

sound Wall solves interstateWidening Problems


TRANSPORTATION

homes Without surround soundWhite springs at Providence, Collegeville, Pabuilder: Toll BrothersContractor: Pickering Valley LandscapeProducer: Fizzano Brothers Concrete ProductsLicensor: Allan Block Company

When creating the upscale, single-family residentialhousing development White Springs at Providence inCollegeville, PA, builder Toll Brothers needed a structuralsound wall that was not only functional in the area ofacoustics, but also attractive enough from the residentialside to entice buyers to the complex. On one side of thewall is a state highway with heavy traffic, traveling at anaverage speed of 55 mph (88.6 km/h), on the other is abrand new development of carriage homes.

e builder, along with the landscape contractor Picker-ing Valley Landscape, Elverson, PA, chose concrete ma-sonry for the privacy wall after much research at varioushome shows throughout the region. e wall also neededto be approved by the township board to meet aestheticcharacteristics and approved by the Pennsylvania Depart-ment of Transportation engineers to meet structural re-quirements. e block system selected passed both tests.

e concrete fence was the right product to meet all thestructural and sound requirements, and had the addedbenefit of being attractive. More than 1,500-feet (457.3-m) long, the wall height averages 8 feet (2.4 m). Con-struction of the carriage homes is still underway, but thesound wall has already been completed. CMD


ends of the new island. These are some of the changes thatcontributed to the cost increase from the original estimate of$14.5 million.

Soon after construction commenced, the general contractortook another look at the precast mechanically stabilized earth(MSE) retaining walls. In consultation with the design-builder, the block producer and the licensor, senior project en-gineer with Prince Contracting Company Thomas Hill said,“We evaluated a segmental block retaining wall system designand construction process as an alternative to conventionalMSE retaining wall construction.”

“At that time, the FDOT was in the process of adding the seg-mental block retaining wall systems to its innovative designslist. After researching and reviewing the new product, Princeproposed the use of the segmental block retaining walls as an

TRANSPORTATION

Cruising Interstate 75

The North Cattlemen Road Extension in SarasotaCounty, FL, is a $20 million transportationimprovement project that connects University Parkway

at its north end with Fruitville Road to the south. With northand south ends of the roadway now joined, local traffic canbypass Interstate 75, and have easier access to some of thearea’s most desirable commercial, recreational and sportingfacilities.

An existing two-lane road was transformed into a four-lanedivided roadway, and the four divided lanes were extended fur-ther north for another 1.75 miles (2.8 km). Funds supplied bythe federal government were administered through the FloridaDepartment of Transportation (FDOT) on behalf of SarasotaCounty. The project encompasses the road, a 96-foot (29.3 m)bridge on Cattlemen Road to Center Island on a 400-acre(162 hectacres) lake, excavation and reconfiguration of a 50-acre (20 hectacres) lake, and two additional bridges to anew island built as part of the road’s program.

But there is also a parallel project underway near the Cattle-men Road site. Sarasota County is creating an extensive recre-ational boating and rowing competition center at the NathanBenderson Park. The Cattlemen Road Extension project in-cluded realigning a land bridge about 300 feet (91.4 m) awayfrom its original location. The move was necessary to expandthe rowing area of the park’s main lake and accommodate2,000-meter (6,561-ft) Olympic-class rowing events, withSarasota’s sights set on hosting the 2017 World RowingChampionships.

“Initially, there were two separate retention ponds detailed oneither side of a faux bridge,” said Alex Boudreau, civil engineerand project manager for Sarasota County Public Works Divi-sion. “Faux,” because it was designed as a causeway to look likea bridge, even though the stormwater ponds were not actuallyconnected hydraulically. But the aesthetic decision was latermade to change that feature to a single body of water flowingunder a bridge. In addition, an idea took hold to build an is-land in the large lake with two span bridges, at east and west

SRWs provide a fast, economical and beautiful solutionto north cattlemen extension.


alternative to the conventional MSE retaining walls,” Hilladded. The contractor convinced Sarasota County and theFDOT to use the new segmental block retaining wall system.

Boudreau says the SRW walls turned out to be much morecost effective. “The modular masonry retaining walls were lesscostly upfront including installation and created a beautifulwall that offered flexibility—the wall could be installed at thesame time other parts of the project were being built,” he said,and it had the same strength characteristics of precast. Hepoints out that the decision to add two more bridges influ-enced the selection of segmental retaining walls. It was a giventhat the look of all three bridges needed to be cohesive, butthere would be a minimum of a one month delay for each pre-cast panel order. Instead, the SRW units could be deliveredquickly and installed.

Hill says, “The segmental block retaining wall system allowedPrince to speed up the project by significantly cutting the shopdrawing review process time frame, as well as shortening thetime of production of the blocks. Additionally, the construc-tion process of the segmental block retaining walls allows thecontractor to get more daily production, as compared to con-ventional MSE retaining walls, on longer walls.”

There was yet another advantage, according to Boudreau—maintenance. The SRW system would come integrally coloredand not require an applied finish. Precast panels would need tobe painted, and frequently repainted. “The paint is decorative,

sure,” he said, “but it is also required to seal the concrete sothat moisture doesn’t penetrate and cause the steel componentsin the system to rust and the rust to show on the surface. Inthe SRW concrete block system the reinforcement and the in-dividual units are held together with synthetic rods. So, there isnothing to rust,” he says.

Switching to SRW units was also a cost savings for the ownerthanks to the ability to use onsite fill material as opposed toimporting expensive select fill. The material available was awell-graded, coarse aggregate with less than 15 percent of fines(material finer than the #200 sieve) with a plasticity index lessthan 6 percent, but it didn’t meet the stringent electrochemicalrequirements to be used with metallic reinforcement.

The project totaled 50,000 square feet (4645 m2) of facing infour bridges with a maximum height of 18 feet (5.5 m). Oncethe walls were completed, erosion protection was added to thefront of the walls to avoid scour due to the water moving infront.

While the park and rowing center are still under construction,this 2.75-mile (4.4 km) roadway improvement project wascompleted in June 2013. The SRW portion was finished inJanuary 2013 and the road opened May 2013. All in all, theCattlemen Road Extension project was a success, saysBoudreau. It moves cars through the area smoothly, relievescongestion on I-75, and is beautiful to look at. Boudreau sayshe and a lot of people in the area take their families on drivesalong the Cattlemen Road Extension, even before the park hasbeen completed. CMD

TRANSPORTATION

Cattlemen road extension sarasota, Fln Owner: Sarasota County/ Benderson Developmentn Design/build Contractor: Associated Construction

Products (ACP), Inc.n General Contractor: Prince Contracting Co. n Producer: Coastal an Oldcastle Companyn Licensor: Anchor Wall Systemsn Geosynthetic Manufacturer: TenCate Geosynthetics


A Pattern for Success

TRANSPORTATION

He was referring to the new South Academy BoulevardRamp at Fort Carson in Colorado Springs, wherebridge abutments are formed by a block–face,

mechanically stabilized earth structure. It was a cost effectiveand structurally proficient solution. In some areas of theproject, segmental retaining walls (SRWs) were proposed aspart of the original bid documents, and in other locationsSRWs were proposed as an alternate to the specified panelMSE walls.

Bennetts, whose company provides geogrid reinforced blockSRW systems as well as precast panel MSE systems, alongwith contractor Max Retaining Walls, was instrumental inconvincing El Paso County and their engineers which systemwas best for this project. The exit ramp was originally designed as a combination of block with sections of precast

panels across the abutment, but could be built more economi-cally using specialty SRW units. In addition, the proposedSRW system would provide a more attractive and seamless appearance.

It can be more expensive to build panel MSE systems than theblock SRWs, and such was the case at the South AcademyBoulevard Ramp. There was an economic advantage for thecontractor to work with a single system. And it would be anadvantage for the county as well. Landscape architects and en-gineers are often comfortable using concrete masonry SRWson smaller walls, but they don’t always consider block MSEwalls for larger projects. Competing retaining wall systems forthe larger projects are typically marketed to construction in-dustry professionals as a single system, but that is not alwaysthe perception with the block systems.

“Some people tend to have a preconceived notion thatmechanically stabilized earth (MSE) segmental block units arenot as structurally sound as other systems, such as precastpanels...”

Dustin bennettsTensar international Corporation, District Manager

broomfield, CO


A few companies have been successful in educating designersand contractors about concrete masonry SRWs with the sin-gle-system approach. The chosen SRW system provides agood solution to grade separation by providing a single sourceapproach. This system approach helps contractors and ownersby offering more than individual block or grid components,but rather the kind of package solution that provides a bettermeans of comparing different MSE wall solutions.

Transportation applications place heavy demands on retainingwalls, so the system’s performance is very important. On theSouth Academy Boulevard Ramp, the 22,500 square feet of(2,090.3 m2) proprietary block and reinforced geogrid offer anexcellent solution. This particular system uses proprietaryconnectors to structurally and mechanically attach the geogridto the concrete block units.

Contractor John Petros of Max Retaining Walls, CommerceCity, CO, said that every block was set by hand and the

pattern worked in conjunction with installation of the geogrid,layer by layer. A layer of geogrid was installed every 2 feet(0.61m) of elevation (every three blocks). The pattern wascomplex, but still the walls grew rapidly.

Petros and his team had to carefully plan the staging of mate-rials. Three pallets of block in three different sizes and colorswould be delivered at a time, blocks set and connected to thegeogrid, and backfill placed. Then empty pallets had to be re-moved, and the next set of blocks, geogrids, connectors andsoil delivered.

Layers of geogrid were installed in these walls, which changedelevation rapidly, up to 30 feet (9.14 m) said Petros. And aunified look achieved by using only one type of retaining wallinstead of two contributes to a transportation project recog-nized for its function and aesthetics. CMD

TRANSPORTATION

south academy Boulevard ramp, Coloradosprings, COn Owner: El Paso County, COn Design-build Contractor: Lawrence Constructionn SRW installer: Max Retaining Wallsn Contractor Producer: Basalite Concrete Productsn Licensor: Tensar International Corporationn Geosynthetics: Tensar International Corporation


ACBs

Erosion Control and Stormwater Management with ACBsArticulating concrete block provide an aestheticallypleasing solution to manage stormwater runoff.

With urban areas expanding, the severity of heavyrainfalls increasing, changing climates causingflooding and polluting waterways, erosion control

of stormwater is a pressing concern. Runoff from heavy rainscan cause severe erosion, site disruption and infrastructuredamage, and also threaten the environment.

Stormwater comes from precipitation events, which mostoften are rainstorms but also include melting snow that makesits way into stormwater systems. Some stormwater seeps intothe ground, although heavy rains in urban locales with largeimpervious areas such as roads, sidewalks, driveways, parkingareas, building roofs, and even some lawns, are most likely togenerate surface runoff. Heavy rains cause the runoff to moveat a high speed and lead to erosion on building sites, alongstreams and river banks, and at shore lines. In addition to thephysical damage inflicted by rapidly flowing stormwater, thatrunoff can send significant volumes of unfiltered water andpollutants picked up along the way to sewers, which dischargeinto and contaminate streams, lakes, and distant waterways.

The two main issues surrounding stormwater are seeminglynot complex: the volume of rainwater falling and the velocityof the runoff. But as impervious surface area increases, there isless ground area available to absorb the rainwater. Less

infiltration and less absorption in turn can lead tounanticipated surface erosion in natural sites as well as wherelandscape is maintained, along with flooding, both on the siteand downstream, and also transport of soil sediments andsurface pollutants to vital waterways.

Left unchecked, stormwater runoff can cause widespreaderosion damage to the areas around water bodies and tocommunities and watersheds. As a result, local, state, andfederal governments are stepping in with recommended bestmanagement practices, standards, and regulations to counterthe problem. The industry is responding with innovativeproducts, systems, and designs.

Controlling source waterOne such system is a matrix of articulating concrete block(ACB), a system used for erosion control that can also be usedas an interlocking pavement comprised of individual concreteblocks. When set together individual ACBs create an armorsystem above a stream bank or shoreline. The system iscomprised of the concrete block cover layer—the armor, one ormore filter sublayers, and the soil base below. The individualunits offer the density, durability, strength, and impact resistanceof a concrete block while at the same time providing a matrix

that is flexible and allows infiltraton. For a detailed discussion ofACBs and Erosion Control, see NCMA TEK 11-09B.

The system is “articulating” because individual blocks can shiftslightly, without unlocking from the matrix, and conform tochanges in the subgrade. There are a number of ACBconfigurations and they all vary in plan, cross section, andlocking mechanisms. Each of these proprietary systems offersflexibility of movement, yet is restrained by virtue of theindividual block geometry, along with additional systemcomponents such as cables, or geotextile ropes. The physicalinterlocking feature provided by the special shapes of ACBsalso allows for expansion and contraction.

Flexible ACB revetment systems are effective because theywill conform to variations in subgrade soils, and as a result,subsoils should be carefully prepared. However, subsoil shiftingis still possible, and so the ability of these revetments to alsoshift, yet still maintain contact with the filter and base, is whatmakes them so successful.

Waterfront areas offer recreational and commercialopportunities and access to natural environments. They alsooffer the potential for erosion, flooding and storm damage, andcan require manmade protection to shield fragile environments,ensure personal safety, and preserve property. ACB revetmentsare an ideal solution under heavy water flow conditions, flashflooding and where high velocities of runoff water are expected.The individual block nature of these systems makes installationaround trees possible and also around and above infrastructuresuch as storm drains and water pipes.

Articulating concrete blocks perform double duty as flexiblerevetment systems that provide effective erosion control atriverbanks and shorelines and can also incorporate plants tomaintain a natural appearance, further assisting in erosion

control. The boat ramp at a waterfront recreation area inKlamath, CA, was rebuilt for just those purposes (see RampingUp in Klamath) and with the new vegetation taking hold, it isdifficult to distinguish hardscape from natural environment.As soil revetment systems, ACBs provide protection tounderlying soil materials. They can solve a wide range oferosion problems and can be installed above or below thewaterline, as either cabled or non-cabled systems. Installationis accomplished by hand placement, or with constructionequipment as pre-assembled mats on top of a filter layer onprepared subgrade.

environmental benefits ofpermeable pavementsOne environmental benefit of ACB erosion-preventionmatrices is the inclusion of vertical cores and spaces in thesystems, which allow plants to grow and water to infiltrate.Properly selected plant species can be installed across the hardsurface of the ACBs, to blend in with the site features andhelp with water purification by absorbing nutrients andbreaking down other pollutants.

The overtopping at Lake LaMoure in North Dakota wasundermining the water body, leading to the destruction of thesoil and causing severe erosion to the lake banks andsurrounding areas (see Erosion Control at Lake LaMoureSpillway). But, a massive ACB installation was able to solvethat problem and control flooding. The system installed over adrainage layer maintains the inherent drainage and treatmentsystems of the soil, reducing water runoff and flooding risks,improving water quality, reducing pollutants, rechargingaquifers, and preventing erosion. With plant matter included,ACBs can also contribute to habitat. All of thesecharacteristics make an ACB system a great candidate for usein sustainable projects where stormwater management is ofconcern and erosion control is a priority.


ACBs

St. john’s CollegeHigh School

(see page 52)

stormwater Management:At the end of this article, participants will be able to:n Describe articulating concrete block and articulating

concrete block mat systems and componentsn Understand erosion at water fronts and river

embankments caused by stormwater runoff and the roleof ACBs in mitigating that erosion and preventingovertopping of adjacent water bodies.

n Explain how unchecked stormwater runoff affectsdownstream water bodies.

n Describe how ACB pavement systems can controlerosion on site and maintain the integrity of the site’senvironment.

CEU: LEARNiNG ObjECT ivES


the aBCs of aCBs ACB systems are most often called upon as an erosion controlmeasure. Articulating concrete blocks are specified as a frontline control system to combat the deterioration of coastalshorelines, riverbanks, piers, bridge abutments, boat ramps,dikes, overflow channels and spillways, among other waterwayfeatures, their local environments, and their habitats. ACB sys-tems are increasingly popular alternatives to cast-in-place con-crete bulkheads and slope paving systems, including riprap.Installation and preservation of vegetation and native plants ispossible in the designed voids within the individual ACB unitsof the systems, softening the appearance, and preserving nativehabitats along shorelines and embankments. That is not possi-ble with most competing material systems.

Several varieties of ACB systems are available: interlocking,cable tied and non-cable tied matrices, and open cell andclosed cell varieties. Open cell units contain open voids withinindividual units that facilitate the placement of aggregateand/or soil with plants. Closed cell units are solid concrete ele-ments, and they too are capable of being planted, allowing veg-etation to grow between adjacent units.

Articulating concrete block systems are easy to install, simpleto produce, and environmentally friendly (see ACB SystemsNCMA TEK 11-9B). ACBs are produced according toASTM D6684, Standard Specification for Materials andManufacture of Articulating Concrete Block (ACB) Revet-ment Systems. They can be made in a variety of shapes andthicknesses, and may even be colored. ACBs have excellent re-sistance to hydraulic shear and overtopping conditions.

Small construction crews can easily install ACB systems wherethe units are placed over a filter layer on top of a prepared sub-grade. The filter protects the subgrade and allows bidirectionalwater penetration. Once installed, the open cell voids or joints between the ACB units are filled with granular material or soil.

Installation methods depend on whether the ACB product iscabled or non-cabled. Cabled interlocking blocks are cast withhorizontal holes so that high-strength cables or ropes (syn-thetic or steel) can be installed through the matrix of blocksbinding them into a monolithic mattress. The cables or ropesare intended only to facilitate placement of the mat, and pro-vide no hydraulic stability or structural value to the ACB mator block system. Assembly of the blocks into mats makes itpossible to install these systems underwater and on steepslopes.

ACBs

Runoff Canal(see page 50)


Several commercially available cable systems can be manuallyplaced on a shoreline or channel, and the cables are then hand-inserted through the holes. An advantage of this process is thatsoil protection revetments with fewer seams can be con-structed. Also, it is easier to hand-place the blocks around a ra-dius or projection on a sloped bank, such as a culvert outlet. Toaccomplish this with pre-assembled ACB mats, custom-shaped mats must be either fabricated elsewhere or piece-worked insertions performed on site. Both approaches requirecareful planning, detailing, and execution in the field.

Non-cabled blocks are manufactured in interlocking shapes toprovide a positively connected matrix that is individuallyhand-placed. The blocks are individually installed according tothe geometry of the product. It is possible to install theseACBs in areas without space for large construction equipment.

ACBs without cables are a good choice where complex sitegeometries and limited access are present. These non-cabledACBs offer comparable shear resistance and some systems canbe specified with a higher percentage of open surface area.These blocks are typically delivered on pallets and hand-placed at the jobsite. Without cables, material costs can be re-duced significantly. ACBs without cables can be constructed invirtually seamless fields.

The hydraulic forces considered in the design of erosion con-trol projects using this technology are hydraulic lift, drag, andimpact. ACBs have demonstrated the ability to resist high ve-locity flows in excess of 25 feet per second (7.6 meters per sec-ond), usually associated with drainage channels, water controlstructures, dam spillways, and fast flowing rivers. While manyof the forces created by water can be readily calculated, partic-ularly uplift and drag, each project application has separate de-sign considerations.

ACBsACBs are not designed to add structural strength to the slopes.The protected slope must be geotechnically stable prior toplacement of surface protection. Known as “flexible revet-ments,” ACB installations should not be placed on slopessteeper than the soil’s natural angle of repose.

Filter layers are always placed under the ACBs. The functionof the filter is critical, as it must retain the soil in place whileletting water pass through without clogging. The filter layermust remain in intimate contact with the block and the soil topreclude soil particles from being transported down the slopebeneath the geotextile. For an optimum erosion control mech-anism with ACBs, multiple filter layers are often requiredabove the subgrade. Only woven monofilament or nonwovenneedle-punched geotextiles should be used in filter applica-tions. The filter layer must have a long-term permeability ca-pable of handling the required volume of water through arestricted surface area equal to the joint area of the articulatingconcrete block. The importance of selecting appropriate sub-grade protection cannot be overstated.

The permeability of the filter layer must always be equal to orgreater than the permeability of the protected soil unless a spe-cial bedding layer is provided. The filter layer needs only to re-tain the majority of particles beneath it, thus creating a filterbridge.

runoff, infiltration andgroundwater levelsWhile erosion control is a primary role of ACB systems, theycan play a role in sustainable design as well. ACB pavementsare increasingly specified by landscape architects and contractors to manage stormwater runoff and encourage on-site infiltration.

ACBs create a permeable pavement system and incorporatewater retention abilities within the profile of the system de-sign. For example, the large arch at the underside of the cus-tom-designed block and gravel base used on the service road atSt. John’s High School (Lesson Plan: Permeable Pavement at St.Johns College High School) provided more storage capacity thanthe school could have achieved with a large storage tank, andthe ACB system kept the water on site, replenishing the localwater supply. The system includes a filter underlayer that al-lows water movement in and out - infiltration and exfiltration- and also maintains the integrity of the soil subgrade. The fil-ter layer can be a geotextile or properly graded aggregate, orboth.

In the past, most stormwater management systems worked bycollecting runoff into tanks, retention ponds or other holdingareas, and transporting it off-site through a network of pipes

St. john’s College High School(see page 52)

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to a stream, waterway, holding tank or retention pond. The re-tention pond slowed the water, and in theory, filtered sedimentand other undesirable contaminants before the runoff was re-leased into a waterway. Slowing down the water flow this wayis beneficial in that it reduces flooding and erosion. But thistraditional approach has drawbacks. One of the most critical isthat the stormwater does not recharge the ground where itfalls. And, the traditional system takes up space that couldotherwise be used by nature or other site design criteria.

The Clean Water Act sets the total maximum daily load ofpollutants that a body of water can receive and still meet safewater quality standards. While sewage along with industrialactivities account for a hefty portion of pollutants, stormwaterrunoff brings nonpoint source (NPS) pollution. NPS comesfrom diverse and scattered sources, picked up as the watertravels on the ground. These NPS pollutants end up in rivers,lakes, wetlands, and coastal waters. The U.S. EnvironmentalProtection Agency (EPA) reports on behalf of the States that“nonpoint source pollution is the leading remaining cause ofwater quality problems. The effects of nonpoint source pollu-tants on specific waters vary and may not always be fully as-sessed. However, we know that these pollutants have harmfuleffects on drinking water supplies, recreation, fisheries, andwildlife.” The water quality standards of the Clean Water Actspecify biological criteria for desired aquatic life, nutrient crite-ria to prevent over enrichment and sediment criteria to limitboth contaminated and uncontaminated sediment. In Florida,an out road drainage ditch was overflowing into neighbors’yards and sending pollutants on to streams and the ocean untilit was reconstructed and a mat system installed (see Revital-ization of a Runoff Canal). Also, NPS pollutants are now beingtrapped on-site through native vegetation incorporated in theACB system.

In rural areas or those places with fields, forests, and other per-vious surface features, rainwater mostly infiltrates into the landwhere it falls, and recharges the groundwater. But in developedurban situations, with more impervious areas, groundwaterrecharging is hampered, and as stormwater runoff travels alongits way to sewers, it is likely to pick up contaminants from

streets, residential properties, industrial activities, and farm andagricultural properties.

According to EPA, when stormwater is absorbed into theground such as at St. John’s High School, the water is naturallyfiltered in part, and ultimately replenishes aquifers or flowsinto streams and rivers. But in developed areas any impervioussurfaces such as pavements and roofs will prevent rainwaterfrom naturally soaking into the ground. Rather, EPA informs,the water runs often at high velocity into storm drains, sewersystems, and drainage ditches, causing erosion of stream banks,flooding of waterways, increasing turbidity (mud that erodesinto the water), creating negative changes in the flow rate ofstreams, leading to animal habitat destruction, and even caus-ing infrastructure disruption.

Encouraging permeable pavements, EPA initiated Low Im-pact Development (LID), a series of measures for strategic sitedesign to control the sources of runoff and promote landscapeplanning for ground infiltration. EPA points out that LID canrestore natural watersheds at an individual property by treatingdirectly at the source of runoff. “The goal,” according to EPA,“is to design a hydrologically functional site that mimics pre-development conditions.”

Most ACB systems can serve as a permeable pavement in lowtraffic locations such as a service road or driveway. When usedas a permeable pavement, the base depths of clean stonethroughout the paved area should be engineered, both for in-filtration and structural abilities. ACBs are a good pavementchoice when aesthetics are a consideration, as the individualunit sizes, configurations, color options, and finishes will com-plement landscape features and building designs.

Hardscape designs and technologies that provide for infiltra-tion and recovery of stormwater and its reuse help ensure abalance in natural hydrology. Articulating concrete blockrevetment systems contribute to good stormwater manage-ment practices and provide erosion protection, enhancing thepotential for urban environments to become self-sustainingand water wise. CMD

ACBs

Klamath(see page 46)


A100-year flood hit Klamath, CA, over the holidaysbetween December 1964 and January 1965, wipingout the original town. Known as the Christmas Eve

Flood, the deluge is estimated to to have caused close to580,000 cubic feet of water per second (16,424 m3/s) to flowthrough the Klamath River, devastating just about everythingin its path. The town shifted its location and the old riversidesite was converted into a recreational boating area.

When notable storms struck again in 1997 and 2005, they werenearly as severe, each flooding the original Klamath TownsiteBoat Ramp and inflicting extensive damage to the boating areaand its launching facility. After a few setbacks, including envi-ronmental reviews and a moratorium for one year to protect anunanticipated high rate of salmon spawning and a fishing indus-

try facing hard economic times, a completely new public boatingrecreation center was approved.

Klamath Townsite Boat Ramp is an extensive hardscape re-construction project. It incorporates large embankments of ar-ticulating concrete block (ACB) with a concrete ramp and

ACBs

Klamath townsite Boat ramp reconstruction, Klamath, Ca n Engineer: Stover Engineering n Contractor: Steelhead Constructorsn Producer: Basalite Concrete Products, LLCn ACb Licensor: Submar, Inc.

IN KLAMATH

Due to high flooding in the area, the town selected ACbsto rebuild a boat ramp and protect the land from erosion.

RAMPING UP

Grasses and nature plants will hide most of the manmade ACB units on the Klamath boat ramp.


ACBs

some riprap. Originally, the project included greater areas ofriprap, but aesthetics and a requirement by the CaliforniaCoastal Commission (CCC) to replace some of the nativevegetation that would be lost during construction led to theinclusion of approximately 4,800 square feet (446 m2) of pro-prietary articulated concrete block mats. “This is a sensitivehabitat and a popular public fishing place,” said Ryan Young,project engineer with Stover Engineering. The California De-partment of Fish and Wildlife, along with the CCC, werelooking for a ramp site to include natural vegetation and havean attractive appearance. “That wouldn’t be possible with allriprap, but was with ACBs,” added Young.

The 4.5-inch (114.5-mm) open cell ACBs were chosen as analternative to 2 tons (1814.37 kg) of riprap for shoreline pro-tection above the mean high water mark, according to Ron Il-lium, P.E., regional engineer with Basalite Concrete Productsin Dixon, CA. The primary idea was to protect against river-bank erosion and reduce the large quantity of riprap thatwould be required if the project was to protect the sensitiveshoreline of the Klamath River just before it discharges intothe Pacific Ocean.

While the old boat ramp was perpendicular to the river, thenew ramp was built at a 60-degree angle heading downstreamto make boat launching easier. This would also provideboaters with a still backwater area during times of high veloc-ity flow and prevent damage to the ramp itself during flood-ing. The California Coastal Commission approved extendingand reorienting the Klamath Townsite Boat Ramp and pavingthe banks with ACBs to provide site stability, minimize ero-sion and maximize boater safety.

Stover Engineering’s design offered a more natural appearancefor the boat ramp project above the average high water markthan would come from riprap alone and addressed the need toprotect the riverbanks against erosion. The ACBs also allowedthe contractor to plant vegetation and still have high erosionprotection against periodic flood events. In the past, the river-bank and boat ramp were compromised when the water eleva-tion exceeded the slope protection, said Illium.

The ACB mats are working as designed and have seen twowinters with no erosion. Vegetation is beginning to take root,and the revetment along the riverbanks of Klamath TownsiteBoat Ramp appears increasingly more natural with passingtime. CMD

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Agrass-lined spillway from the lake had servedLaMoure County, ND, for a number of years. Butwith passing time, the earthen overflow corridor

began to erode, and then heavy flooding two years in a rowcaused extensive damage. Completely rebuilt after a severeflood in 2009, grass on the new earthen spillway never had achance to grow before the flood of 2010 caused rising lakewaters to overflow and wipe out the emergency flood controlcorridor, once again.

A better solution was needed. So, engineers with the NorthDakota Natural Resources Conservation Servicerecommended articulating concrete block (ACBs) to stabilizethe soil in the spillway. They chose an ACB mat system for itsability to prevent erosion, said contractor Mark Sellin,president of Sellin Brothers, Hawley, MN.

One challenging issue today, particularly in the United States,is dam overtopping and the need for spillway protection,thanks in large part to aging infrastructure and the need to resize dams that serve increasingly populated areas. Emergencyspillways must have enough capacity to remove peak flowsduring flood conditions.

ACB mat systems are regularly used to protect river and damembankments and earthen spillways. And while maintainingthe integrity of the soil at Lake LaMoure Spillway was theprimary objective, the open structure inherent to the ACBcells had the added benefit of allowing water to pass throughthe mats, preventing water from pooling and maximizing thepotential for vegetative growth on the emergency floodchannel, and also boosting the overall hydraulic performance.

Sellin Brothers had very limited experience with articulatingconcrete block, according to Sellin. Once before, thecontractor installed an ACB mat system along a riverbank, butit was a small project. By contrast, the Lake LaMoureSpillway, at over 150,000 square feet (13,935 m2) is a verylarge installation. “It wasn’t easy at first, but the system wenttogether like a puzzle and once we figured out the pattern andthe rhythm, installation moved along quickly,” Sellin said. Soquickly, they were able to shave weeks off the time tocompletion and finish ahead of schedule on all phases of thejob. Once they understood the process, Sellin’s crews could lay12 mats an hour during good weather. After the site wasprepared, the original estimate for laying mats was 23 days.

ACBs


However, Sellin Brothers finished in 15 days, averaging 10,000square feet (929 m2) of ACB mats installed per day.

Before the ACB system could be installed, damage to theoverflow channel had to be repaired. The earthen spillway wascut down and smoothed to its base. Once Sellins installed andgraded the clay sub-base of the spillway, a 6-inch (152.4-mm)layer of fine granular material was added, with 4 inches (101.6mm) of rock and then a bi-axial geosynthetic polypropylenewith an ultraviolet coating so it doesn’t degrade with exposureto the sun.

Large cranes removed panels from delivery trucks and placedthem on the spillway at the feet of Sellin’s crews, who guidedplacement of each one. Upgrade trenches along the sides of themats were filled with dirt to help hold the system in place.Each of the flexible mats, approximately 8 feet by 38 feet (2.4 m x 11.6 m), are tied together with steel cables, so thatthey can be moved and placed with a crane directly onto theprepared surface. Once on the surface, the mats are then tied together.

Sellin is proud of the job his company did, and is convincedthat ACBs are a good approach to erosion control. But he hassome advice for other contractors. “Do your homework,” hesays. “The system can be quickly put in and performs wellright away, but the surface preparation must be spot-on.” Foroutstanding results, grading must be very smooth. Sellin reliedon a GPS to keep the slopes smooth and cross-checked ateach step with laser equipment. “You want to avoid problemswith the subgrade,” he said, and that means for the ACBsystems to perform as designed, installation needs to be up topar. CMD

ACBs

lake laMoure auxiliary spillway reconstruction, nD

n Owner: U.S Department of Agriculture Natural ResourcesConservation Service

n Engineer: Natural Resources Conservation Servicen Contractor: Sellin Brothersn Producer: Amcon Block and Precastn Licensor: Submar, Inc.n Geosynthetic Manufacturer: TenCate Geosynthetics


Even in sunny Orlando, FL, the rains come, and whenthey do, flooding is a primary concern. Runoff fromroads and highways flows rapidly through ditches such

as State Road 434 Out Road Canal, installed years ago by theFlorida Department of Transportation (FDOT).

Florida has been regulating stormwater discharge andmanagement since the 1980s with the intention of protecting itssurface waters. The Florida Department of EnvironmentalProtection (FDEP), regional water management districts andlocal governments all have oversight responsibilities forstormwater runoff. FDEP requires 80 to 95 percent reduction inthe annual loads of pollutants from rainwater discharge.Meanwhile, the City of Orlando maintains its streets to keepthem clean, safe and in good repair. The City also ensures thatthe drainage facilities perform as intended and that receivingwater bodies meet state and federal water quality standards.

The aging drainage ditch that served a portion of State Road434 had been eroding over time, according to Dale Mudrak,project engineer with Gregori Construction and Engineering.Local properties in the residential neighborhoods where thewater runs through were threatened with erosion and potentialflooding. In order to prevent further damage, FDOT applied tothe regional water district for a permit to make improvementson the 434 Canal drainage ditch, which serves as a conveyancesystem to channel runoff brought in from the State Road, twoadjacent subdivisions and a lake at its head. That runoffultimately flows into Little Wekiva River and through WekivaRiver Buffer Conservation Area, with its fragile wetlands thatare often flooded in the rainy season. The local water districtofficials recognized the need for improvements to the outdated

infrastructure. However, the contractor was required to includevegetation along the canal bank and maintain the plants for oneyear to mitigate the loss of natural vegetation duringconstruction.

Like much of Florida, the canal banks were mostly sand, so anyrapid flow in the drainage canal would lead to erosion. Flowingstormwater added to the canal from the adjacent residentialproperties causes the erosion to increase, especially in areas withno vegetation or where the area lacks stabilization.

aCBs meet site challenges Ready mixed concrete was first considered for the project, butthere were site restrictions that could not be met with thatsolution. Access to the drainage ditch near the two subdivisionswas restricted; too small to get a ready mixed truck on-site. Inaddition, the FDOT was seeking a sustainable solution allowingplants to grow in the revetment area. “So they went witharticulating concrete block (ACBs) instead of ready mix,”Mudrak said.

ACBs

revitalization of a runoff Canal

state road 434 Out road Canal n Owner: Florida Department of Transportationn Engineering: Florida Department of Transportationn Contractor: Gregory Constructionn Producer and Licensor: International Coastal Revetment

Productsn Geosynthetic Manufacturer: TenCate Geosynthetics

With neighborhoods being threatened with flooding anderosion, Florida Department of Transportation used articulatingconcrete blocks to redirect stormwater runoff.


The proprietary ACBs selected for this 25,000-square-foot(2322-m2) project are 6-inch units (152-mm). They wereinstalled as mats, which required a crane for placement. Mudraksays the contractor got permission from two homeowners tobring in a crane between their properties, and the clearance wasso tight that the crane’s retractable wheels had to be withdrawn.

Steel sheet piles were used across the canal to slow down thespeed of the runoff. When the velocity of the stormwater isdecreased, particles in it have time to settle out on the bottom,helping to clear the water. “The ACBs are extremely importantin periods of high flow after a storm event as water will flowaround or over the sheeting weirs, actually increasing waterspeed,” says Mudrak. When that happens, the ACBs will keepthe bottoms and sides of the canal from eroding away.

The Florida Administrative Code’s Water Resource Implemen-tation Rule sets design criteria for stormwater systems. In situa-tions like the State Road 434, where the runoff discharges intothe conservation area of Wekiva River, the rules require a 95percent reduction in pollutant loads. Water quality is a big issuefor the drainage project and one of the critical factors why FDOT chose ACBs, according to Mudrak.

Technically considered a conveyance system, not a treatmentsystem, the ACBs on the canal actually accomplish some ofboth. The combination of the steel weirs and extensive ACBmats offer some water treatment benefits. By slowing down thewater flow with the steel sheeting, there is less erosion and someof the sediment carried in the runoff has time to settle to thebottom.

As for treatment, the ACBs allow vegetation to grow in theopen cells along the canal’s banks. The vegetation then absorbs

nutrients from the water which cleans it. The open cells on thebottom of the canal allow sand to settle and keep it fromcontinuing down stream. Once established, the naturalvegetation can hide the ACBs that are stabilizing the slopes.The life expectancy of this drainage conveyance system, with itstreatment qualities, is 50 years.

“We see ACBs as one of the solutions to erosion and slopestabilization issues. They are an engineered product and in manycases provide better performance than natural products. Weexpect to see continued lower overall cost utilizing ACBscompared to other products which is due to limited amounts ofnatural resources and the increased cost of trucking them. Thequality of the ACBs combined with design flexibility andproduction sizes—both thickness and mat size—make itpreferred by owners, designers and contractors,” says projectengineer Mudrak. CMD

ACBs

A permeable pavement provided thesolution for stormwater runoff.

When St. John’s College High School’s plans for anew cafeteria addition, outdoor service road, andstudent drop-off area presented a stormwater

runoff challenge, beyond what had originally been anticipated,the civil engineers at Landesign Inc. in Bowie, MD, stepped inwith a solution.

Located in Chevy Chase, DC, the school regularly enduresheavy rains that bring large volumes of runoff, often at highvelocities. With 8,000 square feet (743 m2) of new road areaand another 16,500 square feet (1533 m2) of new roof andpatio surfaces simultaneously sending rainwater to the ground,the engineers and project team determined that the originallyspecified concrete pavement and holding tank were undersizedand would not be adequate. To counter that problem and toalso address the need for a more sustainable solution,Landesign reccomended a runoff drain system that sent thewater to the base of a permeable articulating concreteblock/mat (P-ACB/M) paving surface and allowed most ofthe incidental rainwater to infiltrate into the site.

According to Landesign’s professional civil engineer JeffSelker, manufacturer Ernest Maier introduced a proprietary P-ACB/M system that would alleviate some of the issuesconfronting the project. Ernest Maier’s staff worked closelywith Selker on the school project from beginning to end,helping with everything from design to specifications forbedding materials in order to get the project just right.

As conceived by the designers, the original concrete pavementplan channeled the stormwater runoff down the service roadto the top of a 7,500-gallon (28-m3) underground holdingtank. The runoff water in the tank would then be piped slowlyto daylight then to a retention pond to infiltrate on the site.This system, as originally specified with the imperviousconcrete pavement, would have cost the school about$150,000. It would also be seriously undersized and unable todeal with rainfalls that could easily bring three to four times

ACBs


Lesson Plan at St. John’s College

High School

st. John’s College high schoolChevy Chase, MD n Owner: St. John’s Collegen Engineer: Landesign Inc.n Producer: Ernest Maier, Inc, n Licensor: PaveDrain, LLCn Geosynthetic Manufacturer: TenCate

Geosynthetics


section of the proprietary pavers used in this project have anunderside arch with the hollow area serving as a reservoir tohold stormwater on-site and allowing it to infiltrate into theground. Landesign carefully specified the storage area of thearch to maximize water retention.

Responding to the specific stormwater challenges at St. John's,Landesign engineered a roof drain system that dischargeswater into the base of the permeable pavement system. Thearched storage chamber of each block helps to increase thestorage capacity of the system allowing a slow groundinfiltration that recharges local groundwater levels.

Infiltration tests at the site indicated a soil infiltration rate of0.7 inches per hour (17.78 mm/hr). For the pavement areareceiving water discharge from the roof, Landesign specified abase depth of more than 4 feet (1.2 m) of #2 stone so thatstormwater from adjacent impervious surfaces would not causeoverflow and could be retained and infiltrated on-site,establishing what is effectively a retention and infiltrationpond.

Part of the permeable pavement is a turnaround area wherestudents are dropped off, and the reminder is a delivery roadthat services the cafeteria. Selker says that permeablepavements are not typically used for roadways, although the P-ABC/M system at St. John's probably could handle the

ACBs

more water than its storage capacity. In the end, that extrawater would have made its way to the sewer systems and beensent to waterways, not allowed to infiltrate into the groundon-site, resulting in a failure to comply with regulations andstandards for stormwater management, according to Selker.

By contrast, the P-ACB/M paving system could be sized for amuch greater volume of runoff and provide a $50,000 savingsto St. John's. But, there were potential obstacles to overcome.Selker pointed out that the system had to meet Washington’sDistrict Department of the Environment (DDOE) standards,requiring a favorable initial cost and promise to withstand thetest of time for life-cycle cost, function, and appearance.

According to the DDOE website, 43 percent of land area inthe nation’s Capitol is impervious, so a storm that brings 1.2inches (30 mm) of rain produces about 525 million gallons (2million m3) of stormwater runoff. The Department’s proposedretention standards for construction projects intend to makethe District’s hardscaped areas more river friendly. Therefore,when Landesign brought in the idea of the permeable systemfor St. John's, the DDOE quickly approved the P-ACB/Msystem.

The permeable pavement’s installation required varying basedepths of clean stone throughout the paved service road areato accommodate both roof and surface runoff. The cross

ACBs


American Association of State Highway and TransportationOfficials (AASHTO) H20 truck loads (this standard truck iscommonly used in design and has a total weight 40,000pounds or 20 tons). Because only slow-moving vehicles andsome delivery trucks would use the road, there was littleconcern about the structural performance of the pavementunder fast-moving traffic. The pavement system with itsstone-like appearance also makes it “an aesthetically pleasingproduct,” says Selker. In addition, asphalt and other materialswill expand and contract and eventually crack or show damage,“and when you repair asphalt, or even a concrete pavement, youalways see where the patch is, and that area usually getsdamaged again. With this system, you just remove a block andreplace it, but so far I haven’t heard of any damage,” addsSelker.

The initial capital cost of St. John's College High Schoolpermeable pavement project was $100,000. During the firstyear, the capital cost of infiltrating the water to the site wasreported as $0.167, and by year 20 that cost shrinks to $0.008.

During construction, the site was excavated to the depthsspecified for the stone underlayer, and then a monofilamentgeotextile was laid directly on the subgrade. The stone wasinstalled on the geotextile, compacted and leveled, according tothe manufacturer recommendations. Typically for installationsof this size, large construction equipment is used to lay thepavement in large sections, or mats. But in order to keep thecost down and to minimize congestion on the school grounds,the individual blocks were laid by hand.

Completed last year, the permeable articulating concreteblock/mat system at St. John’s has been performing well,preventing puddles, rapid surface runoff, and erosion. Thestormwater retention system successfully has infiltrated600,000 gallons (2271 m3) of rainfall to the site each year. CMD


Segmental retaining walls afford many advantages,including design flexibility, aesthetics, economics, ease ofinstallation, structural performance and durability. Tofunction as planned, SRWs must be properly designedand installed. Inspection is one means of verifying thatthe project is constructed as designed using thespecified materials.

The 2012 International Building Code, Section 105.2 isbeing adopted by jurisdictions around the county. Thecode requires a building permit for earth retainingstructures over 4 feet (1,219 mm) in total height or less ifthey support a surcharge. In addition, many localbuilding codes or officials require a design prepared by alicensed design professional, although there are locationswithout provisions for engineered design. Where there isno specific requirement, NCMA suggests the guidelinesin the table below. Note that local code or ordinancessupersede industry recommendations. CMD

Q & a n

When does a projectneed a designer?By Gabriela Mariscal, P.E.,Geotechnical EngineerNational Concrete [email protected]

The many applications forsegmental retaining wallsmake them quiteappealing to homeowners,contractors and developers. At what pointdoes an SRW project become toocomplicated as a do-it-yourself project orfor a contractor and require the involvementof a design professional?

Design method Wall height Allowable soil & Recommendedfoundation conditions engineering required

Method 1: Less than 4 ft (1.2 m) from Sand/gravel, silty Use design chart provided by Non-engineered leveling pad to top of wall sands, silt/lean clays SRW system provider.

Method 2: More than 4 ft (1.2 m) from Sand/gravel, silty sands, Have the design section Engineered leveling pad to top of wall silt/lean clays reviewed by a registered

professional.

For tiered walls, if the total combined height is less than 4 feet(1,219 mm), the horizontal spacing between walls (D) is at leasttwice the height of the lower wall (i.e., H < 4 ft (1,219 mm) andD > 2H1), and no surcharges are imposed on the walls, followMethod 1 in Table 1. In all other cases follow Method 2 Table 1.

Where: H1 is the total height of the lower tier and D is thedistance between the front of the lower tier to the front of theupper tier.

DesiGn GuiDanCe FOr seGMental retaininG Walls

H

H

H

D

1

2

Note: H > H1 2

(TEK 18-11B, Table 1)


n Marketplace

have You taken advantage of allthe resourcesavailable on thenCMa web site?

n e-TEKn Bookstore n Design Resources n TEK Technical Information n Research Reports n Metric Design Guidelines n Energy Code Options for

CMUn Sustainability Information n Technical Services n Technical Publications

Database n Fire and Acoustics n Design Awards Program n Marketing Resources n Articles for Print and Radio n Camera Ready Artwork n Fire Safety Materials n Mold Materials n Print Ads n Safety Resources n eSafetyLine Software n Opportunities/Leads n Helpful Links n Fire Safety Associations n Mold Resources n Workforce Development

Visit tODaYwww.ncma.org


Marketplace n

Visit the NCMA Solutions Center for all your design and technical needs:

• e-Tek• e-Details• Design Publications• Codes and Standards• and more.

Your complete resource for concrete masonry units, segmental retainingwalls, articulating concrete block and manufactured stone veneer.

www.ncma.orgClick on the NCMA Solutions Center button!

NCMA SolutionsCenter

NC

MA Solutions

Cente

r


Today, it is estimated that about 50 percent of allsegmental retaining wall (SRW) units are sold through

retail outlets for smaller, gravity wall applications—wallsthat do not rely on internal soil reinforcement. Thecharacteristics and design of some of the most commonsegmental retaining walls used by the constructionindustry vary depending on the site conditions and wallgeometry.

Retaining walls are designed to resist the soil andsurcharge loads supported by the system. Designing aretaining wall involves balancing the resisting forces withthe driving forces to create a stable mass with a marginof safety against failure. When designing a segmentalretaining wall, designers should follow establishedNational Concrete Masonry Association (NCMA) orAmerican Association of State Highway andTransportation Officials’ (AASHTO) methodologies.

nCMa Versus aashtOWhile AASHTO requirements are more conservative thanNCMA’s, the two are similar. There are some keydifferences between the two:

nMinimum Geogrid LengthNCMA 4ft (1.2 m) or 0.6H whichever is greaterAASHTO 8ft (2.4 m) or 0.7H whichever is greater

AASHTO specifications based the minimum 8 foot(2.4m) length on experience and ability to getconstruction equipment in behind the wall to compactthe soil. The 0.7H was also based on experience withsteel reinforcing. NCMA designs are based on geogridreinforcing with 100 percent coverage (better pulloutcapacity), thus the 0.6H has worked well for commondesign scenarios.

n Load on the Reinforcement, TMAXWhile NCMA always uses the Coulomb EarthPressures approach, factoring the slope, wall frictionand wall batter into the equation, thus reducing theload (Tmax) in the reinforcing layers compared with anAASHTO design that only uses Coulomb EarthPressures for walls above 10˚ face batter and RankineEarth Pressures below 10˚.

n Reinforced Fill Soil Types.NCMA allows for the use of materials having amaximum 35 percent passing the #200 (75 µm) sieve,and suggests that materials with greater percentage offines may be used when a geotechnical engineer isinvolved. AASHTO restricts use of materials for thereinforced fill zone and requires granular materials withless than 15 percent passing the #200 (75 µm) sieve.

n ConnectionNCMA uses the maximum geogrid load (Tmax) withfactor of safety of 1.5 and compares this to the PeakConnection Capacity between the geosynthetic and

srW history articles series:

srW DesiGn

n srW history

Internal Compound Stability Analysis Example

srW Design:At the end of this article, participants will be able to:n Understand how masonry gravity segmental retaining

walls are detailed and how they differ from mechanicallystabilized earth (MSE) walls with a structural face ofconcrete masonry blocks (SRW).

n Describe bearing capacity, soil base and embedment,and the affect of slope on them.

n Approach the design of multi-depth and multi-tieredwalls, especially for slope-restricted sites usingsegmental retaining wall (SRW) concrete blocks.

n Understand the requirements of mechanically stabilizedearth walls, and the approach to soil stability.

CEU: LEARNiNG ObjECT ivES


SRW unit. AASHTO also uses a factor of safety of 1.5on Tmax; however, AASHTO also requires anadditional reduction factor to be applied to the PeakConnection Capacity that is derived from long-term,sustained load connection testing. This is a veryconservative assumption and not justified byperformance or data from instrumented structuresthat indicates the conservatism inherent in currentSRW design methods.

nOverturningNCMA has suggested a factor of safety of overturning(ability of the structure to resist rotating forward) of1.5 for gravity walls and 2.0 for MSE structures. InAASHTO LRFD (2012), eccentricity is specified (thelocation of the load resultant with respect to thecenter of the footing, L) as e/L < 0.33. The resultantshould be within the middle 1/3 of the base. e/Lyields about the same design as a factor of safety of 2would using the NCMA methodology.

n Seismic DesignBoth NCMA and AASHTO methods use theMononobe-Okabe methods for pseudo static design.Both also assume the total dynamic stress is evenlydistributed over all the layers of reinforcing. NCMA,however, promotes the use of seismic design inseismically active zones, where AASHTO does notconsider seismic design mandatory in zones 1-3 unlessliquefaction induced lateral spreading seismicallyinduced slope failure, due to the presence of sensitive

clays that lose strength during seismic shaking, mayimpact the stability of the wall or if the wall supportsanother structure that is required by code orspecification to be designed for seismic loading andpoor seismic performance could impact the structure.

This article is excerpted from the SRW History ArticleSeries: SRW Design. The complete article can be foundon the NCMA website at www.ncma.org/SRWHistoryDesignArticle which includes more detailed informationabout the equations, design methodolgy for building anddifferent retaining wall types. There are also test questionsafter the article for continuing education credits. CMD

srW history n

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Forces and geometry for external stability analysis of convential SRWs


NCMA Design Manual for Segmental Retaining Walls(3rd edition, 2009).

The dry cast panels are produced on a paver machineand have a high compressive strength of 8500 psi. Dueto the high compressive strength, this panel respondswell under harsh environments and provides long-termdurability. There is also economy for the installers of theMega-Tandem panels as well because each 2-square footpanel weighs 65 pounds and can easily be installed in thefield without heavy equipment.

n new Product Profile

CarVeD in stOnethe Mega-tandem Wall advantage

Belgard Hardscapes has just launched its Mega-Tandem Wall, a new innovation in the segmental

retaining wall (SRW) market. Mega-Tandem can be usedfor residential and commercial applications. Walls may bebuilt up to 10-feet (3 m) high without reinforcement and15-feet (4.5 m) high with reinforcement.

These 12-inch by 24-inch (0.31m x 0.61m) flat blocks areunique in that they provide the rustic look of large, hand-cut stones, but without all the heft. They can be used asan alternative to conventional retaining walls, precast bigblock, and where reinforced SRWs cannot beaccommodated due to space limitations. In addition, theaesthetics are outstanding. Mega-Tandem offers thedesigner the look of natural stone with the economics ofan SRW.

These new blocks operate similarly to conventionalsegmental retaining wall units, providing the requiredinterlock. The blocks are created by attaching two veneerpanels with a reinforced polypropylene mechanicalconnector and filled with aggregates for weight andstructural integrity. It is the gravel fill inside the wall,between the two block faces, that provides the stabilityexpected of an SRW system. The Mega-Tandem systemcan be designed following the methodology of the

aDVertOrial

Design Versatility

7

Maximum Gravity Wall Height System Setback Minimum Radius

6' with 27" connector 10' with 46" connector 2.5° 16'

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With finished faces on two wall sides possible, thisretaining wall system offers a number of designopportunities for freestanding walls as well as retainingwalls. Design versatility allows for radiuses andengineered right angle corners with a 2.5-degreesetback. The face of Mega-Tandem has a texturereminiscent of natural stone. The Mega-Tandem wall’srear panel can be specified with a ground face, shotblasted texture, or the more traditional look of smoothfederal stone.

For specifications, view technical data from BelgardHardscapes at https://s3.amazonaws.com/BelgardCommercial/MegaTandem/MegaTandemSpecification.pdfand for a detailed product design chart from Oldcastle athttp://s3.amazonaws.com/Belgard Commercial/MegaTandem/13-130+Mega+Tandem+Design+Charts+ 040213+Final.pdf

new Product Profile n

Mega – Tandem Wall Installation

•!Slide panels into jigs •!Place connecting members into dove tail slots

•!Connecting members are placed into middle slot to the outside panel edge

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Installation Detail

41

Typical 10 foot high wall Assembly unit

Corner unit

Cut to fit

Corner unit cut to fit

Full face unit

Typical 6 foot high wall assembly unit

Cut to fit Typical 6 foot high wall assembly unit

Geotextile fabric

Cut unit

Connector 1 required per face foot

Full face unit

Infill material #57 stone Corner face cut to fit

Installation Detail

39

Backfill material

Connector 2 per face foot on typical wall assembly unit

Infill material #57 stone

Typical wall assembly unit Front face

Excavation limits

Foundation block Leveling sand

Base foundation

Leveling sand

Foundation block

Infill material #57 stone

Geotextile fabric

Earth

Excavation limits

Back face

aDVertOrial


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Learning objectives:Readers of the listed article will:• Learn to describe a segmental retaining wall and

its components• Understand settlement and how backfill and

geogrid stabilize SRWs• Explain the height limits for tall SRWs• Discuss the design considerations for tall SRW

walls in creating additional horizontal spaceabove.

1. Concrete masonry segmental retaining walls (SRWs) are a system of interlockingunits thata) Are dry stacked block walls intended to

hold back a soil slope and may be built at atrue vertical

b) Are dry stacked concrete masonry wallsthat resist the lateral forces of backfill soils

c) Are comprised of foundation soil, levelingpad, mortar, retained soil, gravel fill, andsoil reinforcement

d) a & be) a, b & c

2. The unit-to-unit interface and inherent mass of SRWs a) Resist overturning and sliding through the

force mechanisms of friction, shear, andinterlock.

b) Built with concrete block units alone do notprovide sufficient strength for taller walls

c) a & bd) None of the above

3. Segmental retaining walls are consideredflexible concrete masonry structures, so afooting must be placed below the frost lineand there must be sufficient foundationbearing capacity. a) Trueb) False

4. Layout issues and tolerances, such as thewall batter and geosynthetic reinforcementlengths, are the same for both low gravitywalls and tall, reinforced walls.a) Trueb) False

5. Various synthetic products are on the marketto help stabilize a tall segmental retainingwall. This tieback component of tall SRWs a) Must be buried in backfillb) Is called a geogridc) Varies in length according to the increasing

height of the walld) all of the abovee) none of the above

6. Post-construction settlement of reinforced infill soil is only of concern during wall designwhen backfill settlement is anticipated to begreater than 10 percent of the fill height.a) Trueb) False

7. Total reinforced soil settlement, even in minorpercentages, adds up over the height of a tallwall. Such settlement of wall backfillnegatively affects a) The interlocking mechanism of the wallb) The performance of any structures above

the wall, such as pavements and possiblystresses their geosynthetics

c) The performance of any structures abovethe wall, such as pavements and possiblystresses their geosynthetics, although itdoes not overload the unit to reinforcementconnection.

d) None of the above

8. Segmental retaining wall backfill settlementcan be countered by avoiding soilcompaction and increasing leveling activitiesand quality control.a) Trueb) False

9. To minimize settlement for higher walls, gravel filla) Should be uniform in thickness, from top to

bottomb) Thicker at the top than the bottomc) Thicker at the bottom than the topd) Replaced with lighter soilse) Not used

10. To increase stability in tiered walls, the tieredsections should be set as far apart from oneanother as possiblea) Trueb) False

Tall Walls Questions (Circle the correct answer)

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Learning objectives:Readers of the listed article will:• Describe articulating concrete block and

articulating concrete block mat systems andcomponents

• Understand erosion at water fronts and riverembankments caused by stormwater runoff andthe role of ACBs in mitigating that erosion andpreventing overtopping of adjacent water bodies.

• Explain how unchecked stormwater runoff affectsdownstream water bodies.

• Describe how ACB pavement systems cancontrol erosion on site and maintain the integrityof the site’s environment.

1. The water quality standards of the CleanWater Act specify biological criteria to limitall sediment.a) Trueb) False

2. Articulating concrete blocks a) Are flexible revetment systems that can

incorporate plants to maintain a naturalappearance

b) Interfere with natural habitats and shouldonly be used for traffic areas

c) Are buried a few feet below the surface toencourage vegetation growth above

d) All of the above

3. ACBs can solve a wide range of erosion problems and can be installed above orbelow the water line as a) Cabled mat systems placed by hand b) Non-cabled mat systems placed by hand or

cabled mat systems placed by machinec) Non-cabled systems placed by machine

4. Mats of ACBs are often used to protect riverand dam embankments and earthenspillways and these revetments havedemonstrated the ability to resist velocityflows as high as a) 25 feet per second (7.6 m/s)b) 35 feet per second (10.6 m/s)c) 45 feet per second (13.7 m/s)

5. ACBs used as pavements are suitable fortraffic areas, driveways and roadwaysa) Trueb) False

6. Urban development and pavement contributeto rainwater runoff responsible for a) surface erosion b) onsite filtering of sedimentc) flooding on site and downstreamd) a & be) a & c

7. Individual blocks in an ACB system arelocked rigidly together, do not shift andcreate a single plane of protection for thesubgradea) Trueb) False

8. ACBs installed on filter media reduce waterrunoff and flooding risks, improve waterquality, reduce pollutants, recharge aquifersand prevent erosion. a) These environmental characteristics permit

the use of ACBs in sustainabledevelopments to preserve or improveexisting sites, or in new developments.

b) Meet the criteria to be used for Low ImpactDevelopment

c) Control stormwater runoff by mimickingpre-development conditions

d) None of the abovee) All of the above

9. Runoff drain systems that employ ACBpermeable pavements and accommodategroundwater recharging area) Most important in rural areasb) Aimed at keeping the local water table

charged and reducing runoff from the site c) Sends pollutants away from the sited) None of the above

10. The permeability of ACB matrices results innatural drainage and off-site water treatmentcapabilitiesa) Trueb) False

Stormwater Control Questions (Circle the correct answer)

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To receive one learning unit, read “Erosion Control and Stormwater Management with ABCs,” and com-plete the questions on this page. Return this form to receive a learning unit credit. To receive AIA learningcredits, this quiz must be received by December 31, 2014.


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Learning objectives:Readers of the listed article will:• Understand how masonry gravity segmental

retaining walls are detailed and how they differfrom mechanically stabilized earth (MSE) wallswith a structural face of concrete masonry blocks(SRW).

• Describe bearing capacity, soil base andembedment, and the affect of slope on them.

• Approach the design of multi-depth and multi-tiered walls, especially for slope-restricted sitesusing segmental retaining wall (SRW) concreteblocks.

• Understand the requirements of mechanicallystabilized earth walls, and the approach to soilstability.

1. The typical design height for most gravity walls is a) 3 to 4 feet (0.91 to 0.21 meters)b) 5 to 6 feet (1.52 to 1.82 meters)c) 10 feet (3.01 meters)

2. When considering the driving and theresisting moments on an SRW, the minimumoverturning safety factor for wall designshould be:a) 1.5 or aboveb) 1.9 or abovec) 1.9 or below

3. In evaluating the global stability of walls onslopes, tier walls, or walls on unstablefoundations, a factor of safety between 1.3and 1.5 is sufficient.a) Trueb) False

4. For the design of SRW multi-depth and multi-tiered segmental retaining walls, therecommended wall height limit is:a) 20 feet (6.09 meters)b) 35 feet (10.67 meters)c) 50 feet (15.25 meters)d) 20 feet each tier (6.09 meters)e) unlimited

5. Mechanically stabilized earth structures withSRW facing walls can be built only to amaximum height of 25 feet.a) Trueb) False

6. Multi-depth SRWs units have anchors andtrunks attached to the facing units to givemore depth to the wall structure. As a result,the weight of the SRW units must be factoredin, but weight of the gravel fill is notconsidered, except for its bearing capacity.a) Trueb) False

7. Low strength permeable concrete is amaterial thata) Contains both fines and larger aggregateb) Lets water drain through the SRWc) Provides structural mass sufficient for a

larger concrete retaining wall, while theSRW facing adds the aesthetics desired.

d) Both a & be) Both b &c

8. SRW MSE walls need geosynthetics (geogridor geofabrics) to maintain wall batter, butcannot exceed 30 feet (9.14 meters) in heighta) Trueb) False

9. In SRW design, the spacing of geosyntheticreinforcement is determined to avoid ruptureof the connection between the reinforcementand the SRW units fora) calculating quantity of gravel backfill b) facial stability analysisc) determining post spacing

10. Both NCMA and AASHTO promote the use ofseismic design in a) all seismic zones b) seismic zones 1 through 3c) neither a nor b

SRW History Questions (Circle the correct answer)

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To receive one learning unit, read “SRW Design” in the SRW History Article Series, and complete thequestions on this page. Return this form to receive a learning unit credit. To receive AIA learningcredits, this quiz must be received by December 31, 2014.

ACB, SRW, and Hardscape Resources from NCMADesign Manual for Articulating Concrete Block, 2nd EditionThis comprehensive new manual covers the design and construction of articulating concrete block (ACB ) systems, which provide erosion protection to the underlying soil from the hydraulic forces of moving water. Per the latest FHWA publication, Bridge Scour and Stream Instability

standards for ACBs. 97 pages. (2010). (NCMA item number TR220A)Member: $25.00 ........................ Professional: $35.00 ................................ Retail: $50.00

Articulating Concrete Block (ACB) Design Spreadsheet Articulating Concrete Block (ACB) Design Spreadsheet, based on NCMA’s new ACB design manual. Also includes riprap sizing to compare erosion control methods. (2011). (NCMA item number TR220AS)Free on request by emailing to [email protected] .

Design Manual for Segmental Retaining Walls, 3rd EditionEssential guides to aid designers, both the manual and software have been fully updated to include the latest design methodology for both gravity and soil-reinforced earth walls. The manual includes design criteria, design tables, illustrations, installation procedures and sample

previously published as separate documents. 293 pages (2009). (NCMA item number TR127B)Member: $99.00 ........................ Professional: $139.00 ............................ Retail: $198.00

Design Software for Segmental Retaining Walls30 day free trial download. SR Wall Version 4 covers design of both conventional gravity and soil reinforced walls in accordance with NCMA ’s Third Edition Design Manual for Segmental Retaining Walls, TR 127B. Users are highly encouraged to read the manual before using the program. Viewable PDF included with purchase of software. Windows XP or newer (2009). Discounts for upgrades and combination offers with Design Manual. (NCMA item number SRWallv4)Full working free 30-day trial version available at www.ncma.org.Member: $325.00 ....................... Professional: $450.00 ............................ Retail: $650.00

Segmental Retaining Wall Installation Guide

Design Manual for Segmental Retaining Walls. This document is ideal to educate SRW contractors and owners on the proper techniques for installing segmental retaining wall systems. It includes technical information regarding excavation, geosynthetic grids, best industry practices and more. 32 pages. (2010). (NCMA item number TR 146A)Member: $6.00 ........................... Professional: $8.40 .................................. Retail: $12.00

NCMA TEK Notes SeriesTEK 2-4B Segmental Retaining Wall Units TEK 6-9C CM and Hardscape Products in LEEDTM 2009 TEK 11-9B Articulated Concrete Block for Erosion ControlTEK 11-12A ACB Revetment Design - Factor of Safety Method TEK 11-13 Articulating Concrete Block (ACB) Installation TEK 15-3A Roles and Responsibilities on SRW ProjectsTEK 15-4B Segmental Retaining Wall Gobal StabilityTEK 15-7B Concrete Masonry Cantilever Retaining WallsTEK 15-8B Guide to Segmental Retaining Walls TEK 15-9A Seismic Design of Segmental Retaining Walls TEK 18-10 Sampling and Testing Segmental Retaining Wall UnitsTEK 18-11A Inspection Guide for Segmental Retaining Walls Member: $0.95 ........................... Professional: $1.35 .................................... Retail: $1.90

Technical HotlineNCMA provides a full-time staff engineer to answer questions and respond to inquiries on a daily basis. For immediate attention please call 703-713-1900 or 877-627-3976, or email [email protected].

More Available at www.ncma.org:

SRW and ACB Producer Members and SRW

Contractor Members

Certified SRW Installers

Basic & Advanced (CSRWI & CSRWI-A)

Segmental Retaining Wall Installer Trainers

NCMA Bookstore

Information on Webinars, Classes, Seminars, and

Hands-on Training

TEK Notes & Details

Magazines, Project Profiles, Photos, AIA

Quizes, and More!

A n i n f o r m a t i o n s e r i e s f r o m t h e n a t i o n a l a u t h o r i t y o n c o n c r e t e m a s o n r y t e c h n o l o g y

ARTICULATING CONCRETE BLOCKFOR EROSION CONTROL TEK 11-09B

Articulating Concrete Blocks (ACBs) (2011)

INTRODUCTION

An articulating concrete block (ACB) system is a matrix of individual concrete blocks placed together to

occur while providing particle retention of the soil sub-

or properly graded aggregate or both. The blocks within the matrix must be dense and durable while providing a

Articulating concrete block systems are used to pro-vide protection to underlying soil materials. The term "articulating" implies the ability of individual blocks of the system to conform to changes in subgrade while

remaining interlocked or otherwise restrained by virtue of the block geometric interlock and/or additional system components such as cables, ropes, geotextiles, or geogrids. The interlocking property provided by the special shapes of ACBs also allows for expansion and contraction. Long-term durability and sustainability relies on an appropriate

geotechnical conditions. They are either hand-placed or

prepared subgrade, and act as a soil revetment. Articulating concrete blocks (ACBs) are an effective erosion control system used to solve a wide variety of erosion problems:

Related TEK:6-9C, 11-12

Keywords: ACBs, articulating concrete block, construc-tion, techniques, durability, erosion control, grid pavers

Stream Channelization, Before and After ACB Installation


INSPECTION GUIDE FOR SEGMENTAL RETAINING WALLS

TEK 18-11AQuality Assurance and Testing (2010)

INTRODUCTION

Segmental retaining walls (SRWs) are gravity retaining -

--

-

Design Manual for Segmental Retaining Walls

INSPECTION

SRW UNIT PROPERTIES

Retaining Wall Units

Segmental

Related TEK: Keywords:


ROLES AND RESPONSIBILITIESON SEGMENTAL RETAINING WALL PROJECTS

TEK 15-3AStructural (2010)

INTRODUCTION

On all construction projects, including those in-volving segmental retaining walls (SRWs), it is the owner’s responsibility to achieve coordination between construction and design professionals that ensures all required design, engineering analysis, and inspection is provided. In many cases, a design professional such as a site civil engineer or an architect acts as the owner’s representative. In either case, the owner or owner’s representative should ensure that the engineering design professionals' scope of work, roles and responsibilities

-ing responsibility for investigation, analysis and design, and that all required testing is performed. The roles outlined in this TEK are typical industry roles for various engineering disciplines. SRW design and construction should generally follow these traditional roles. However, these roles may vary from project to project, depend-ing on the contractual obliga-tions of each consultant. For example, for simpler projects, such as residential landscapes, one design professional may take on the responsibility of several roles, if acceptable to local building code require-ments.

For tall or complex walls and for commercial projects, each of these roles is likely to be provided by separate

discussion in this TEK is generally oriented towards proj-ects where several design professionals are contracted. Reinforced SRWs, because of their nature as composite soil structures, may have unique design and inspection considerations for the site civil engineer, the geotechnical engineer, and the independent testing agency. These considerations are discussed in further detail in the following sections.

Related TEK:8-1A, 8-2A, 8-3A, 8-4A, 18-11A

Keywords: contracts, construction, design, details, inspec-tion, maintenance, responsibilities, roles, scope of work, segmental retaining walls, soils, SRW, stability, testing

Wallheight = H

Foundation soil

SRW units

Cap unit (optional)

Drainage swale (optional)

Low permeability soil

Compacted reinforced (infill)soil zone

Compacted common backfill

Slope for positive drainage

Setback/batter

Finished grade

Retained Soil Zone

Geosynthetic reinforcement

Gravel fill

Limit of excavation

Drainage collection pipe

Leveling pad

Figure 1—Reinforced Segmental Retaining Wall System Components

Mosaic Random Face Patterns

Freestanding Walls

Fully Integrated Stairs

Random-Pattern Tall Walls

Freestanding Columns

Multi-Angle Corners

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Concrete Masonry


13750 Sunrise Valley DriveHerndon, VA 20171-4662

A PUbLiCATiON OF

WWW.NCMA.ORG

Documents

Designing with SRWs and ACBs - ncma-br.orgncma-br.org/pdfs/masterlibrary/CMD 2013 hardscapeLR.pdfDesigning with SRWs and ACBs . The complete ﬂashing system that keeps your masonry